fix(authentication): system lang separator

[ShGKme]

@nextcloud/l10n expect _ separator while OS may return -.

🖼️ Screenshots

🏚️ Before	🏡 After
de-DE	de_DE

[ShGKme]

Thanks @Dtrieb for catching the issue

[nickvergessen]

For inspiration:
https://github.com/nextcloud/server/blob/1bf15da86343b8213a8554fcf3cda78a9000b455/lib/private/L10N/Factory.php#L480-L535

We could also fall back from dialects to base language (e.g. when de_AT is configured we could use de)

Not sure you can check that, but can also be done in a follow up

[ShGKme]

For inspiration: https://github.com/nextcloud/server/blob/1bf15da86343b8213a8554fcf3cda78a9000b455/lib/private/L10N/Factory.php#L480-L535

We could also fall back from dialects to base language (e.g. when de_AT is configured we could use de)

Not sure you can check that, but can also be done in a follow up

Done

[ShGKme]

However, there is a translation issue for informal German...

https://github.com/nextcloud/talk-desktop/blob/672cb5a34dd43e71b20e5f56e541ceefda830228/l10n/de.json

[nickvergessen]

Right... So either we tell translators that this is not like the normal desktop client and they should translate both, or we remap de_DE to de on translation sync like in the files client

[ShGKme]

Right... So either we tell translators that this is not like the normal desktop client and they should translate both, or we remap de_DE to de on translation sync like in the files client

On https://help.nextcloud.com/t/list-of-resources-and-their-priority-for-translation/78312#mobile-clients-4 it is said

Follows the language pattern of the web apps, therefore translations should be available for all server supported languages, e.g. de and de_DE

Discussing this with the translator.

[ShGKme]

• Rebased onto master to include fixed German translations from translators
• Fixed a small typo: talk -> spreed in app name in translations

Tested with @Dtrieb