update_weblate_git: langs.json &isWikiPo

I made some small mistakes to fix #16449 (closed), and the merge stategy does not work. Those two fixes should now make it working in the end.

It now loads correctly langs.json from /var/lib/weblate/scripts/config/langs.json and fixes:

FileNotFoundError: [Errno 2] No such file or directory: '/var/lib/weblate/scripts/langs.json'

also fixing the issue, that isWikiPo does not detect po files in src/wiki.

Feature Branch: https://salsa.debian.org/hefee/puppet-tails/tree/hefee/dev/translation-server

Parent Task: #10034 (closed)

Original created by @Hefee on 16487 (Redmine)