Improve translation strings for Welsh

[shuuji3]

The string "moved_title": "has indicated that their new account is now:" can't really be translated
It is assumed that the article can be placed first but in Welsh it would have to be "Mae x wedi" for "x has".
The same is true for strings such as "favourited_post": "favorited your post".
It is workable but ugly to leave it as it is, fixing this would require re-writing all translation files, a task I do not feel up to.

#1236 (comment)

We can probably add a prefix string and let them be empty strings for other languages. Example on Mastodon web UI: https://mastodon.social/@shuuji3?lang=cy