[fix] move locale code from webapp.py to locales.py and fix #1303

To improve modularization this patch:

- moves *locale* related implementation from the webapp.py application to the
  locale.py module.

- The initialization of the locales is now done in the application (webapp) and
  is no longer done while importing searx.locales.

In the searx.locales module a new dictionary named `LOCALE_BEST_MATCH` has been
added.  In this dictionary we can map languages without a translation to
languages we have a translation for.

To fix #1303 zh-HK has been mapped to zh-Hant-TW (we do not need additional
translations of traditional Chinese)

Closes: https://github.com/searxng/searxng/issues/1303
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

1 files changed, 104 insertions, 26 deletions

diff --git a/searx/locales.py b/searx/locales.py
index 677b13334..fbdf305ad 100644
--- a/searx/locales.py
+++ b/searx/locales.py
@@ -9,61 +9,139 @@ import os
 import pathlib
 
 from babel import Locale
+from babel.support import Translations
+import flask_babel
+import flask
+from flask.ctx import has_request_context
+from searx import logger
 
-LOCALE_NAMES = {
+logger = logger.getChild('locales')
+
+
+# safe before monkey patching flask_babel.get_translations
+_flask_babel_get_translations = flask_babel.get_translations
+
+LOCALE_NAMES = {}
+"""Mapping of locales and their description.  Locales e.g. 'fr' or 'pt-BR' (see
+:py:obj:`locales_initialize`)."""
+
+RTL_LOCALES: Set[str] = set()
+"""List of *Right-To-Left* locales e.g. 'he' or 'fa-IR' (see
+:py:obj:`locales_initialize`)."""
+
+ADDITIONAL_TRANSLATIONS = {
     "oc": "Occitan",
-    "nl-BE": "Vlaams (Dutch, Belgium)",
     "szl": "Ślōnski (Silesian)",
 }
-"""Mapping of locales and their description.  Locales e.g. 'fr' or 'pt-BR'
-(delimiter is *underline* '-')"""
+"""Additional languages SearXNG has translations for but not supported by
+python-babel (see :py:obj:`locales_initialize`)."""
 
-RTL_LOCALES: Set[str] = set()
-"""List of *Right-To-Left* locales e.g. 'he' or 'fa-IR' (delimiter is
-*underline* '-')"""
+LOCALE_BEST_MATCH = {
+    "oc": 'fr-FR',
+    "szl": "pl",
+    "nl-BE": "nl",
+    "zh-HK": "zh-Hant-TW",
+}
+"""Map a locale we do not have a translations for to a locale we have a
+translation for. By example: use Taiwan version of the translation for Hong
+Kong."""
 
 
-def _get_name(locale, language_code):
-    language_name = locale.get_language_name(language_code).capitalize()
-    if language_name and ('a' <= language_name[0] <= 'z'):
-        language_name = language_name.capitalize()
-    terrirtory_name = locale.get_territory_name(language_code)
-    return language_name, terrirtory_name
+def localeselector():
+    locale = 'en'
+    if has_request_context():
+        value = flask.request.preferences.get_value('locale')
+        if value:
+            locale = value
+
+    # first, set the language that is not supported by babel
+    if locale in ADDITIONAL_TRANSLATIONS:
+        flask.request.form['use-translation'] = locale
+
+    # second, map locale to a value python-babel supports
+    locale = LOCALE_BEST_MATCH.get(locale, locale)
+
+    if locale == '':
+        # if there is an error loading the preferences
+        # the locale is going to be ''
+        locale = 'en'
+
+    # babel uses underscore instead of hyphen.
+    locale = locale.replace('-', '_')
+    return locale
+
+
+def get_translations():
+    """Monkey patch of flask_babel.get_translations"""
+    if has_request_context() and flask.request.form.get('use-translation') == 'oc':
+        babel_ext = flask_babel.current_app.extensions['babel']
+        return Translations.load(next(babel_ext.translation_directories), 'oc')
+    if has_request_context() and flask.request.form.get('use-translation') == 'szl':
+        babel_ext = flask_babel.current_app.extensions['babel']
+        return Translations.load(next(babel_ext.translation_directories), 'szl')
+    return _flask_babel_get_translations()
 
 
-def _get_locale_name(locale, locale_name):
+def get_locale_descr(locale, locale_name):
     """Get locale name e.g. 'Français - fr' or 'Português (Brasil) - pt-BR'
 
     :param locale: instance of :py:class:`Locale`
     :param locale_name: name e.g. 'fr'  or 'pt_BR' (delimiter is *underscore*)
     """
-    native_language, native_territory = _get_name(locale, locale_name)
-    english_language, english_territory = _get_name(locale, 'en')
+
+    native_language, native_territory = _get_locale_descr(locale, locale_name)
+    english_language, english_territory = _get_locale_descr(locale, 'en')
+
     if native_territory == english_territory:
         english_territory = None
+
     if not native_territory and not english_territory:
         if native_language == english_language:
             return native_language
         return native_language + ' (' + english_language + ')'
+
     result = native_language + ', ' + native_territory + ' (' + english_language
     if english_territory:
         return result + ', ' + english_territory + ')'
     return result + ')'
 
 
-def initialize_locales(directory):
-    """Initialize global names :py:obj:`LOCALE_NAMES`, :py:obj:`RTL_LOCALES`."""
+def _get_locale_descr(locale, language_code):
+    language_name = locale.get_language_name(language_code).capitalize()
+    if language_name and ('a' <= language_name[0] <= 'z'):
+        language_name = language_name.capitalize()
+    terrirtory_name = locale.get_territory_name(language_code)
+    return language_name, terrirtory_name
+
+
+def locales_initialize(directory=None):
+    """Initialize locales environment of the SearXNG session.
+
+    - monkey patch :py:obj:`flask_babel.get_translations` by :obj:py:`get_translations`
+    - init global names :py:obj:`LOCALE_NAMES`, :py:obj:`RTL_LOCALES`
+    """
+
+    directory = directory or pathlib.Path(__file__).parent / 'translations'
+    logger.debug("locales_initialize: %s", directory)
+    flask_babel.get_translations = get_translations
+
+    for tag, descr in ADDITIONAL_TRANSLATIONS.items():
+        LOCALE_NAMES[tag] = descr
+
+    for tag in LOCALE_BEST_MATCH:
+        descr = LOCALE_NAMES.get(tag)
+        if not descr:
+            locale = Locale.parse(tag, sep='-')
+            LOCALE_NAMES[tag] = get_locale_descr(locale, tag.replace('-', '_'))
+
     for dirname in sorted(os.listdir(directory)):
         # Based on https://flask-babel.tkte.ch/_modules/flask_babel.html#Babel.list_translations
         if not os.path.isdir(os.path.join(directory, dirname, 'LC_MESSAGES')):
             continue
-        locale_name = dirname.replace('_', '-')
-        info = LOCALE_NAMES.get(locale_name)
-        if not info:
+        tag = dirname.replace('_', '-')
+        descr = LOCALE_NAMES.get(tag)
+        if not descr:
             locale = Locale.parse(dirname)
-            LOCALE_NAMES[locale_name] = _get_locale_name(locale, dirname)
+            LOCALE_NAMES[tag] = get_locale_descr(locale, dirname)
             if locale.text_direction == 'rtl':
-                RTL_LOCALES.add(locale_name)
-
-
-initialize_locales(pathlib.Path(__file__).parent / 'translations')
+                RTL_LOCALES.add(tag)