About [[MediaWiki:Tooltip-iwiki/cy]]
My translation of MediaWiki:Tooltip-iwiki/cy is not being saved.
It's not saved because you've inserted the exactly same text from the definition. Sounds like a feature preventing the user to save the translation with no changes, but IMHO it works as a bug on situations like this one.
To bypass that issue I usually send "_" or another random character as translation and in a next edit I change the text to the correct one.
It's for bugzilla:52223