For English and German, it's easy, 1: singular, everything else: plural. For other languages, there are sometimes multiple plural forms, e.g. in Russian, we have 1: singular; 2-5, 21-25, 31-35, etc.: plural1; 6-20, 26-30, etc.: plural2. We should probably use the gettext library or similar for this, they already implement that. They're also a superset of our current translation system, so the transition should be somewhat easy.

This uses GTest as a test framework.

This is supported on Windows (https://docs.microsoft.com/en-us/cpp/c-runtime-library/printf-p-positional-parameters) and on POSIX, so basically everywhere. Add some tests to verify that the target system does indeed support these positional parameters.

48129f0 Add possibility to test - heinrich5991 97febe4 Add status message for missing GTest - heinrich5991 ae36f37 Automatically download GTest on Windows - heinrich5991 cb88718 Run the tests on CircleCI - heinrich5991 1064ee4 Run tests on AppVeyor - heinrich5991

ddd2b93 Allow translations to reorder string substitutions - heinrich5991 508f56f Merge pull request #2032 from heinrich5991/pr_p... - oy

fdc14f0 added a config option for old gcc compilers whi... - oy e6170cd Merge branch 'master' of https://github.com/tee... - oy

d0294db let SDL use the X11 XRandR window manager per d... - oy

732b003 Add -msse2 to compile flags on x86 only if nece... - heinrich5991 8e8e05c Merge pull request #2033 from heinrich5991/pr_c... - oy