SI: Translations of tests

[janezd]

Bad news:

• We will have to run tests on translated Orange, too.
• Just marking some tests as language-dependent won't do: there would be too many of them and I've seen bugs that we would overlook if we just skipped tests. Hence, we will need to translate tests as well.

I wanted to avoid adding strings from tests to translations because it would (almost exactly) double the file length. Therefore I've put them in a separate file, which is to be treated by different standards: the actual translations should (in principle) have no null's, while for tests nulls are OK - we only translate what is necessary.

Besides translations for tests, this PR includes some other small fixes.