[l10n] Document how far Material-UI should go

docs/src/pages/guides/localization/localization.md

@@ -61,7 +61,10 @@ const theme = createMuiTheme({
 
 You can [find the source](https://github.com/mui-org/material-ui/blob/master/packages/material-ui/src/locale/index.js) in the GitHub repository.
 
-To create your own translation, or to customise the English text, copy this file to your project, make any changes needed and import the locale from there. (Please do consider contributing new translations back to Material-UI by opening a pull request.)
+To create your own translation, or to customise the English text, copy this file to your project, make any changes needed and import the locale from there.
+
+Please do consider contributing new translations back to Material-UI by opening a pull request.
+However, Material-UI aims to support the [100 most popular locales](https://en.wikipedia.org/wiki/List_of_languages_by_number_of_native_speakers), we might not accept contributions for locales that are not frequently used, for instance `gl-ES` that has "only" 2.5 million native speakers.
 
 ### Example
 

packages/material-ui/src/locale/index.ts

@@ -594,6 +594,55 @@ export const frFR: Localization = {
   },
 };
 
+export const glES: Localization = {
+  props: {
+    MuiBreadcrumbs: {
+      expandText: 'Mostrar camiño',
+    },
+    MuiTablePagination: {
+      backIconButtonText: 'Páxina anterior',
+      labelRowsPerPage: 'Filas por páxina:',
+      labelDisplayedRows: ({ from, to, count }) => `${from}-${to === -1 ? count : to} de ${count}`,
+      nextIconButtonText: 'Seguinte páxina',
+    },
+    MuiRating: {
+      getLabelText: (value) => `${value} Estrela${value !== 1 ? 's' : ''}`,
+      emptyLabelText: 'Baleira',
+    },
+    MuiAutocomplete: {
+      clearText: 'Limpar',
+      closeText: 'Pechar',
+      loadingText: 'Cargando…',
+      noOptionsText: 'Sen opcións',
+      openText: 'Aberto',
+    },
+    MuiAlert: {
+      closeText: 'Pechar',
+    },
+    MuiPagination: {
+      'aria-label': 'Paxinador',
+      getItemAriaLabel: (type, page, selected) => {
+        if (type === 'page') {
+          return `${selected ? '' : 'Ir á '}páxina ${page}`;
+        }
+        if (type === 'first') {
+          return 'Ir á primeira páxina';
+        }
+        if (type === 'last') {
+          return 'Ir á última páxina';
+        }
+        if (type === 'next') {
+          return 'Ir á páxina seguinte';
+        }
+        if (type === 'previous') {
+          return 'Ir á páxina anterior';
+        }
+        return undefined;
+      },
+    },
+  },
+};
+
 export const heIL: Localization = {
   props: {
     // MuiBreadcrumbs: {