diff --git a/general/conftest.py b/general/conftest.py
new file mode 100644
index 00000000000..8b11707a8a0
--- /dev/null
+++ b/general/conftest.py
@@ -0,0 +1,7 @@
+"""Settings for pytest tests"""
+
+import os
+
+# The tests are written for English messages, so they would fail in a
+# translated locale, e.g., when running on a system which is not English.
+os.environ["LANGUAGE"] = "C"
diff --git a/general/g.region/printwindow.c b/general/g.region/printwindow.c
index 865e33b5ae1..9f38b94f632 100644
--- a/general/g.region/printwindow.c
+++ b/general/g.region/printwindow.c
@@ -108,7 +108,9 @@ void print_window(struct Cell_head *window, int print_flag, int flat_flag,
 
     /* flag.print & flag.gprint */
     if (print_flag & PRINT_REG) {
-        prj = G_database_projection_name();
+        /* machine-readable output must not depend on the locale */
+        prj = format == PLAIN ? G_database_projection_name()
+                              : G_database_projection_name_untranslated();
         if (!prj && format != JSON)
             prj = "** unknown **";
 
diff --git a/imagery/conftest.py b/imagery/conftest.py
new file mode 100644
index 00000000000..8b11707a8a0
--- /dev/null
+++ b/imagery/conftest.py
@@ -0,0 +1,7 @@
+"""Settings for pytest tests"""
+
+import os
+
+# The tests are written for English messages, so they would fail in a
+# translated locale, e.g., when running on a system which is not English.
+os.environ["LANGUAGE"] = "C"
diff --git a/include/grass/defs/gis.h b/include/grass/defs/gis.h
index 106c9801ef4..fc9be60243a 100644
--- a/include/grass/defs/gis.h
+++ b/include/grass/defs/gis.h
@@ -714,11 +714,13 @@ int G_projection(void);
 /* proj2.c */
 int G_projection_units(int);
 const char *G_projection_name(int);
+const char *G_projection_name_untranslated(int);
 
 /* proj3.c */
 const char *G_database_unit_name(int);
 int G_database_unit(void);
 const char *G_database_projection_name(void);
+const char *G_database_projection_name_untranslated(void);
 const char *G_database_datum_name(void);
 const char *G_database_ellipse_name(void);
 double G_database_units_to_meters_factor(void);
@@ -846,6 +848,7 @@ void G_trim_decimal(char *);
 double G_meters_to_units_factor(int);
 double G_meters_to_units_factor_sq(int);
 const char *G_get_units_name(int, int, int);
+const char *G_get_units_name_untranslated(int, int, int);
 int G_units(const char *);
 int G_is_units_type_spatial(int);
 int G_is_units_type_temporal(int);
diff --git a/lib/conftest.py b/lib/conftest.py
new file mode 100644
index 00000000000..8b11707a8a0
--- /dev/null
+++ b/lib/conftest.py
@@ -0,0 +1,7 @@
+"""Settings for pytest tests"""
+
+import os
+
+# The tests are written for English messages, so they would fail in a
+# translated locale, e.g., when running on a system which is not English.
+os.environ["LANGUAGE"] = "C"
diff --git a/lib/gis/proj2.c b/lib/gis/proj2.c
index a971ecc545f..9ece2f1b7d0 100644
--- a/lib/gis/proj2.c
+++ b/lib/gis/proj2.c
@@ -45,6 +45,9 @@ int G_projection_units(int n)
 /*!
    \brief Get projection name
 
+   The name is translated, so it is meant for messages and other text for
+   people. Use G_projection_name_untranslated() for machine-readable output.
+
    \param n projection code
 
    \return projection name
@@ -65,3 +68,30 @@ const char *G_projection_name(int n)
         return NULL;
     }
 }
+
+/*!
+   \brief Get projection name in English, independent of the locale
+
+   Same as G_projection_name(), but never translated, so the result is
+   suitable for machine-readable output (JSON, shell style).
+
+   \param n projection code
+
+   \return projection name
+   \return NULL on error
+ */
+const char *G_projection_name_untranslated(int n)
+{
+    switch (n) {
+    case PROJECTION_XY:
+        return "x,y";
+    case PROJECTION_UTM:
+        return "UTM";
+    case PROJECTION_LL:
+        return "Latitude-Longitude";
+    case PROJECTION_OTHER:
+        return "Other Projection";
+    default:
+        return NULL;
+    }
+}
diff --git a/lib/gis/proj3.c b/lib/gis/proj3.c
index 4c1491452c4..ca52b34dce4 100644
--- a/lib/gis/proj3.c
+++ b/lib/gis/proj3.c
@@ -132,6 +132,33 @@ const char *G_database_projection_name(void)
     return name;
 }
 
+/*!
+   \brief Get projection name for the current location in English
+
+   Same as G_database_projection_name(), but never translated, so the result
+   is suitable for machine-readable output (JSON, shell style).
+
+   \return projection name
+ */
+const char *G_database_projection_name_untranslated(void)
+{
+    int n;
+    const char *name;
+
+    switch (n = G_projection()) {
+    case PROJECTION_XY:
+    case PROJECTION_UTM:
+    case PROJECTION_LL:
+        return G_projection_name_untranslated(n);
+    }
+
+    name = lookup_proj("name");
+    if (!name)
+        return "Unknown projection";
+
+    return name;
+}
+
 /*!
    \brief Conversion to meters
 
@@ -161,7 +188,8 @@ double G_database_units_to_meters_factor(void)
     if (buf)
         sscanf(buf, "%lf", &factor);
     if (factor <= 0.0) {
-        unit = G_database_unit_name(0);
+        /* the table has English names, so the translated name does not match */
+        unit = G_get_units_name_untranslated(G_database_unit(), 0, FALSE);
         for (n = 0; table[n].unit; n++)
             if (equal(unit, table[n].unit)) {
                 factor = table[n].factor;
diff --git a/lib/gis/units.c b/lib/gis/units.c
index f3256bf9cbe..004093c6538 100644
--- a/lib/gis/units.c
+++ b/lib/gis/units.c
@@ -178,209 +178,236 @@ int G_is_units_type_temporal(int units)
     return 0;
 }
 
-/*!
-   \brief Get localized units name
-
-   Units codes (gis.h):
-   - U_METERS
-   - U_KILOMETERS
-   - U_ACRES
-   - U_HECTARES
-   - U_MILES
-   - U_FEET
-   - U_USFEET
-
-   \param units units code
-   \param plural plural form if true
-   \param square area units if true
-
-   \return units name
-   \return NULL if units not found
- */
-const char *G_get_units_name(int units, int plural, int square)
+static const char *units_name(int units, int plural, int square, int localize)
 {
     switch (units) {
     case U_UNKNOWN:
         if (square)
             return plural
                        // GTC: localized area units
-                       ? _("square units")
+                       ? (localize ? _("square units") : "square units")
                        // GTC: localized area units
-                       : _("square unit");
+                       : (localize ? _("square unit") : "square unit");
         else
             return plural
                        // GTC: localized units
-                       ? _("units")
+                       ? (localize ? _("units") : "units")
                        // GTC: localized units
-                       : _("unit");
+                       : (localize ? _("unit") : "unit");
         break;
 
     case U_METERS:
         if (square)
             return plural
                        // GTC: localized area units
-                       ? _("square meters")
+                       ? (localize ? _("square meters") : "square meters")
                        // GTC: localized area units
-                       : _("square meter");
+                       : (localize ? _("square meter") : "square meter");
         else
             return plural
                        // GTC: localized units
-                       ? _("meters")
+                       ? (localize ? _("meters") : "meters")
                        // GTC: localized units
-                       : _("meter");
+                       : (localize ? _("meter") : "meter");
         break;
 
     case U_KILOMETERS:
         if (square)
             return plural
                        // GTC: localized area units
-                       ? _("square kilometers")
+                       ? (localize ? _("square kilometers")
+                                   : "square kilometers")
                        // GTC: localized area units
-                       : _("square kilometer");
+                       : (localize ? _("square kilometer")
+                                   : "square kilometer");
         else
             return plural
                        // GTC: localized units
-                       ? _("kilometers")
+                       ? (localize ? _("kilometers") : "kilometers")
                        // GTC: localized units
-                       : _("kilometer");
+                       : (localize ? _("kilometer") : "kilometer");
         break;
 
     case U_ACRES:
         if (square)
             return plural
                        // GTC: localized area units
-                       ? _("acres")
+                       ? (localize ? _("acres") : "acres")
                        // GTC: localized area units
-                       : _("acre");
+                       : (localize ? _("acre") : "acre");
         else
-            return G_get_units_name(G_units(G_database_unit_name(1)), plural,
-                                    square);
+            return units_name(G_database_unit(), plural, square, localize);
         break;
 
     case U_HECTARES:
         if (square)
             return plural
                        // GTC: localized area units
-                       ? _("hectares")
+                       ? (localize ? _("hectares") : "hectares")
                        // GTC: localized area units
-                       : _("hectare");
+                       : (localize ? _("hectare") : "hectare");
         else
-            return G_get_units_name(G_units(G_database_unit_name(1)), plural,
-                                    square);
+            return units_name(G_database_unit(), plural, square, localize);
         break;
 
     case U_MILES:
         if (square)
             return plural
                        // GTC: localized area units
-                       ? _("square miles")
+                       ? (localize ? _("square miles") : "square miles")
                        // GTC: localized area units
-                       : _("square mile");
+                       : (localize ? _("square mile") : "square mile");
         else
             return plural
                        // GTC: localized units
-                       ? _("miles")
+                       ? (localize ? _("miles") : "miles")
                        // GTC: localized units
-                       : _("mile");
+                       : (localize ? _("mile") : "mile");
         break;
 
     case U_FEET:
         if (square)
             return plural
                        // GTC: localized area units, do not confuse with US feet
-                       ? _("square feet")
+                       ? (localize ? _("square feet") : "square feet")
                        // GTC: localized area units, do not confuse with US foot
-                       : _("square foot");
+                       : (localize ? _("square foot") : "square foot");
         else
             return plural
                        // GTC: localized units, do not confuse with US feet
-                       ? _("feet")
+                       ? (localize ? _("feet") : "feet")
                        // GTC: localized units, do not confuse with US foot
-                       : _("foot");
+                       : (localize ? _("foot") : "foot");
         break;
 
     case U_USFEET:
         if (square)
             return plural
                        // GTC: localized area units, do not confuse with feet
-                       ? _("square US feet")
+                       ? (localize ? _("square US feet") : "square US feet")
                        // GTC: localized area units, do not confuse with foot
-                       : _("square US foot");
+                       : (localize ? _("square US foot") : "square US foot");
         else
             return plural
                        // GTC: localized units, do not confuse with feet
-                       ? _("US feet")
+                       ? (localize ? _("US feet") : "US feet")
                        // GTC: localized units, do not confuse with foot
-                       : _("US foot");
+                       : (localize ? _("US foot") : "US foot");
         break;
 
     case U_DEGREES:
         if (square)
             return plural
                        // GTC: localized area units
-                       ? _("square degrees")
+                       ? (localize ? _("square degrees") : "square degrees")
                        // GTC: localized area units
-                       : _("square degree");
+                       : (localize ? _("square degree") : "square degree");
         else
             return plural
                        // GTC: localized units
-                       ? _("degrees")
+                       ? (localize ? _("degrees") : "degrees")
                        // GTC: localized units
-                       : _("degree");
+                       : (localize ? _("degree") : "degree");
         break;
 
     case U_YEARS:
         return plural
                    // GTC: localized time units
-                   ? _("years")
+                   ? (localize ? _("years") : "years")
                    // GTC: localized time units
-                   : _("year");
+                   : (localize ? _("year") : "year");
         break;
 
     case U_MONTHS:
         return plural
                    // GTC: localized time units
-                   ? _("months")
+                   ? (localize ? _("months") : "months")
                    // GTC: localized time units
-                   : _("month");
+                   : (localize ? _("month") : "month");
         break;
 
     case U_DAYS:
         return plural
                    // GTC: localized time units
-                   ? _("days")
+                   ? (localize ? _("days") : "days")
                    // GTC: localized time units
-                   : _("day");
+                   : (localize ? _("day") : "day");
         break;
 
     case U_HOURS:
         return plural
                    // GTC: localized time units
-                   ? _("hours")
+                   ? (localize ? _("hours") : "hours")
                    // GTC: localized time units
-                   : _("hour");
+                   : (localize ? _("hour") : "hour");
         break;
 
     case U_MINUTES:
         return plural
                    // GTC: localized time units
-                   ? _("minutes")
+                   ? (localize ? _("minutes") : "minutes")
                    // GTC: localized time units
-                   : _("minute");
+                   : (localize ? _("minute") : "minute");
         break;
 
     case U_SECONDS:
         return plural
                    // GTC: localized time units
-                   ? _("seconds")
+                   ? (localize ? _("seconds") : "seconds")
                    // GTC: localized time units
-                   : _("second");
+                   : (localize ? _("second") : "second");
         break;
     }
 
     return NULL;
 }
 
+/*!
+   \brief Get localized units name
+
+   Units codes (gis.h):
+   - U_METERS
+   - U_KILOMETERS
+   - U_ACRES
+   - U_HECTARES
+   - U_MILES
+   - U_FEET
+   - U_USFEET
+
+   The name is translated, so it is meant for messages and other text for
+   people. Use G_get_units_name_untranslated() for machine-readable output.
+
+   \param units units code
+   \param plural plural form if true
+   \param square area units if true
+
+   \return units name
+   \return NULL if units not found
+ */
+const char *G_get_units_name(int units, int plural, int square)
+{
+    return units_name(units, plural, square, 1);
+}
+
+/*!
+   \brief Get units name in English, independent of the locale
+
+   Same as G_get_units_name(), but never translated, so the result is suitable
+   for machine-readable output (JSON, shell style) and for comparison with
+   names which G_units() recognizes.
+
+   \param units units code
+   \param plural plural form if true
+   \param square area units if true
+
+   \return units name
+   \return NULL if units not found
+ */
+const char *G_get_units_name_untranslated(int units, int plural, int square)
+{
+    return units_name(units, plural, square, 0);
+}
+
 /*!
    \brief Get units code by name
 
@@ -404,7 +431,7 @@ const char *G_get_units_name(int units, int plural, int square)
 int G_units(const char *units_name)
 {
     if (units_name == NULL) {
-        return G_units(G_database_unit_name(1));
+        return G_database_unit();
     }
 
     if (strcasecmp(units_name, "meter") == 0 ||
diff --git a/lib/raster3d/headerinfo.c b/lib/raster3d/headerinfo.c
index d89f9ec372d..2a8729488c5 100644
--- a/lib/raster3d/headerinfo.c
+++ b/lib/raster3d/headerinfo.c
@@ -239,6 +239,8 @@ int Rast3d_get_vertical_unit2(RASTER3D_Map *map)
  * \brief
  *
  * Return the name of the unit of <em>map</em>. Units are defined in gis.h.
+ * The name is in English, whatever the locale, because it is used in
+ * machine-readable output and in files.
  *
  * Vertical units may have temporal type
  *
@@ -247,7 +249,7 @@ int Rast3d_get_vertical_unit2(RASTER3D_Map *map)
  */
 const char *Rast3d_get_vertical_unit(RASTER3D_Map *map)
 {
-    return G_get_units_name(map->vertical_unit, 1, 0);
+    return G_get_units_name_untranslated(map->vertical_unit, 1, 0);
 }
 
 /*---------------------------------------------------------------------------*/
diff --git a/misc/m.measure/main.c b/misc/m.measure/main.c
index 32851e61b84..4db17f1d7c6 100644
--- a/misc/m.measure/main.c
+++ b/misc/m.measure/main.c
@@ -37,6 +37,7 @@ int main(int argc, char **argv)
     double length, area, f, sq_f;
     int i, npoints;
     const char *units_name, *sq_units_name;
+    int unit_id;
     enum OutputFormat format;
     G_JSON_Value *root_value = NULL;
     G_JSON_Object *root_object = NULL;
@@ -114,14 +115,18 @@ int main(int argc, char **argv)
         y[i] = atof(coords->answers[2 * i + 1]);
     }
 
-    /* determine units */
-    if (G_projection() == PROJECTION_LL && !units->answer) {
-        units_name = G_get_units_name(U_METERS, 1, 0);
-        sq_units_name = G_get_units_name(U_METERS, 1, 1);
+    /* determine units; only the plain output is for people, so only it gets
+     * translated names */
+    unit_id = (G_projection() == PROJECTION_LL && !units->answer)
+                  ? U_METERS
+                  : G_units(units->answer);
+    if (format == PLAIN) {
+        units_name = G_get_units_name(unit_id, 1, 0);
+        sq_units_name = G_get_units_name(unit_id, 1, 1);
     }
     else {
-        units_name = G_get_units_name(G_units(units->answer), 1, 0);
-        sq_units_name = G_get_units_name(G_units(units->answer), 1, 1);
+        units_name = G_get_units_name_untranslated(unit_id, 1, 0);
+        sq_units_name = G_get_units_name_untranslated(unit_id, 1, 1);
     }
     f = G_meters_to_units_factor(G_units(units->answer));
     sq_f = G_meters_to_units_factor_sq(G_units(units->answer));
diff --git a/python/conftest.py b/python/conftest.py
new file mode 100644
index 00000000000..8b11707a8a0
--- /dev/null
+++ b/python/conftest.py
@@ -0,0 +1,7 @@
+"""Settings for pytest tests"""
+
+import os
+
+# The tests are written for English messages, so they would fail in a
+# translated locale, e.g., when running on a system which is not English.
+os.environ["LANGUAGE"] = "C"
diff --git a/python/grass/gunittest/invoker.py b/python/grass/gunittest/invoker.py
index 7805902c7bd..712400e722c 100644
--- a/python/grass/gunittest/invoker.py
+++ b/python/grass/gunittest/invoker.py
@@ -166,6 +166,8 @@ def _run_test_module(
         env["GISRC"] = gisrc
         # percentage in plain format is 0...10...20... ...100
         env["GRASS_MESSAGE_FORMAT"] = "plain"
+        # tests check English messages, whatever the locale of the caller
+        env["LANGUAGE"] = "C"
 
         stdout_path = os.path.join(cwd, "stdout.txt")
         stderr_path = os.path.join(cwd, "stderr.txt")
diff --git a/python/grass/gunittest/main.py b/python/grass/gunittest/main.py
index f8458ec93d1..83986a88d92 100644
--- a/python/grass/gunittest/main.py
+++ b/python/grass/gunittest/main.py
@@ -107,6 +107,10 @@ def test():
     #    pass
     # TODO: add some message somewhere
 
+    # tests check English messages, whatever the locale of the caller; the
+    # invoker sets this too, but a test file can also be run directly
+    os.environ["LANGUAGE"] = "C"
+
     # TODO: enable passing omit to exclude also gunittest or nothing
     program = GrassTestProgram(
         module="__main__", exit_at_end=False, grass_location="all"
diff --git a/raster/conftest.py b/raster/conftest.py
index 88b6d553686..e07a0427945 100644
--- a/raster/conftest.py
+++ b/raster/conftest.py
@@ -12,6 +12,11 @@
 from grass.experimental import TemporaryMapsetSession
 
 
+# The tests are written for English messages, so they would fail in a
+# translated locale, e.g., when running on a system which is not English.
+os.environ["LANGUAGE"] = "C"
+
+
 @pytest.fixture(scope="module")
 def session_with_raster_for_module(tmp_path_factory):
     """Active session with CRS and raster data"""
diff --git a/scripts/conftest.py b/scripts/conftest.py
index d96ac31ee97..5e241ee14c7 100644
--- a/scripts/conftest.py
+++ b/scripts/conftest.py
@@ -14,6 +14,11 @@
 from grass.experimental import TemporaryMapsetSession
 
 
+# The tests are written for English messages, so they would fail in a
+# translated locale, e.g., when running on a system which is not English.
+os.environ["LANGUAGE"] = "C"
+
+
 @pytest.fixture(scope="module")
 def monkeypatch_module() -> Generator[pytest.MonkeyPatch]:
     """Yield a monkeypatch context, through a module-scoped fixture"""
diff --git a/temporal/conftest.py b/temporal/conftest.py
new file mode 100644
index 00000000000..8b11707a8a0
--- /dev/null
+++ b/temporal/conftest.py
@@ -0,0 +1,7 @@
+"""Settings for pytest tests"""
+
+import os
+
+# The tests are written for English messages, so they would fail in a
+# translated locale, e.g., when running on a system which is not English.
+os.environ["LANGUAGE"] = "C"
diff --git a/vector/conftest.py b/vector/conftest.py
index c183dd0be08..1dffba74493 100644
--- a/vector/conftest.py
+++ b/vector/conftest.py
@@ -6,6 +6,11 @@
 import grass.script as gs
 
 
+# The tests are written for English messages, so they would fail in a
+# translated locale, e.g., when running on a system which is not English.
+os.environ["LANGUAGE"] = "C"
+
+
 @pytest.fixture
 def xy_dataset_session(tmp_path):
     """Creates a session with XY project"""