Option to switch between translation sets on every page

[La-Geek]

If you translate e. g. german default,you will see no information whether you are editing the standard or informal strings (screenshot point 3).

Also, it would be great if you could switch between formal and default on each page (screenshot point 4)

(Screenshot Point 2 was mentioned in #884, and Point 1 in #883)

The switch would also be absolutely optimal somewhere in the translation window of a single string:

[ocean90]

Default/formal/informal/etc are translation sets, changed the title to reflect that.

[martin8032]

This switch should not only include de_DE informal and de_DE formal but also all translation sets of de_CH and de_AT as well.