Add translations missing in 1.8.0
Note that the following keys haven't been translated because I'm not sure
a translation would really be better then the original strings:
* _decimal_points
* _thousands_separator
* _thousands_suffix
* _millions_suffix
* add translations missing in Q2A 1.8.0
* reorder some translations to match the order of they of the en files
(it makes it easier to spot missing translations)
Note that the string for caching_dir_public hasn't been translated because
the usage of this key has actually been removed from Q2A
(see https://github.com/q2a/question2answer/pull/721 for more context)
* add some translations for 1.8.0
* add a whitespace before ':'
* fix a dubious translation
* reorder some lines to match the order of the en lang file
(it makes it easier to spot missing translations)
