[hotfix] Revert "[bugfix] localize welcome message and support channel invite"
This reverts commit 9d6cf506.
Reasoning:
- Localizing these notifications was premature, since we don't expose the functionality to create non-English channels to users yet
- It also created nasty merge conflicts for ongoing work in !521 (merged)
- So: we revert this commit and leave the work of both creating non-English channels and notifying users about them in non-English languages to #445 (in which we leave a reference to this commit as a friendly breadcrumb)