System settings search keywords

[Fòram na Gàidhlig]

There is a whole bunch of new strings that look like this:

TRANSLATORS: This is a keyword or name for the language plugin which is
used while searching

Now, we have "words", for example. In English, this will match both
"word" and "words" nicely. In ma language, I will have to decide if
users can search for "facal". "facail" or "faclan".

This is also obvious is you look at english "photo", "picture", "image"
- we have 3 synonyms here. What if it's the other way around and my
languages has multiple synonyms for a search keyword, but English doesn't?