gui: Switch to Weblate for translations (#8777)

* Normalize EOL before EOF.

* Import current Transifex state, only translated.

Skip duplicated and completely empty languages.

* Re-add untranslated strings to JSON files.

These are now treated correctly as untranslated, but present with the
original (English) translation key.

* Update valid language codes and names.

* Refer to Weblate instead of Transifex for translations.

* lang-es: Copy untranslated strings from es-ES.

* Integrate translation changes from Weblate.

Translated using Weblate (Polish)

Currently translated at 100.0% (512 of 512 strings)

Translation: Syncthing/GUI strings
Translate-URL: https://hosted.weblate.org/projects/syncthing/gui/pl/

Translated using Weblate (Danish)

Currently translated at 98.6% (505 of 512 strings)

Translation: Syncthing/GUI strings
Translate-URL: https://hosted.weblate.org/projects/syncthing/gui/da/

Translated using Weblate (Lithuanian)

Currently translated at 85.4% (441 of 516 strings)

Translation: Syncthing/GUI strings
Translate-URL: https://hosted.weblate.org/projects/syncthing/gui/lt/

Translated using Weblate (French)

Currently translated at 100.0% (516 of 516 strings)

Translation: Syncthing/GUI strings
Translate-URL: https://hosted.weblate.org/projects/syncthing/gui/fr/

Translated using Weblate (Danish)

Currently translated at 98.6% (509 of 516 strings)

Translation: Syncthing/GUI strings
Translate-URL: https://hosted.weblate.org/projects/syncthing/gui/da/

Translated using Weblate (Spanish)

Currently translated at 100.0% (516 of 516 strings)

Translation: Syncthing/GUI strings
Translate-URL: https://hosted.weblate.org/projects/syncthing/gui/es/

* translation update uses weblate

---------

Co-authored-by: Jakob Borg <jakob@kastelo.net>

CONTRIBUTING.md

@@ -24,10 +24,15 @@ too much information will never get you yelled at. :)
 ## Contributing Translations
 
 All translations are done via
-[Transifex](https://www.transifex.com/projects/p/syncthing/). If you
-wish to contribute to a translation, just head over there and sign up.
+[Weblate](https://hosted.weblate.org/projects/syncthing/). If you wish
+to contribute to a translation, just head over there and sign up.
 Before every release, the language resources are updated from the
-latest info on Transifex.
+latest info on Weblate.
+
+Note that the previously used service at
+[Transifex](https://www.transifex.com/projects/p/syncthing/) is being
+retired and we kindly ask you to sign up on Weblate for continued
+involvement.
 
 ## Contributing Code