While questions could vary in language, the tags have to be in one language for obvious reasons. Tag synonyms would work fine, but we'd have to decide whether German tags should point to English tags or vice versa.
After thinking a while I came to the decision that promoting german use at maximum may be the best possibility:
As an platform formed out of mostly english natives and less german natives our primary concern should be to attract as many german experts and intermedians as possible. There will never be a lack of non-natives asking about meanings of german words or needing help. However the community giving the answers needs to be attracted to.
Therefore we should have strong bounds and good questions targeted on german natives. Choosing our tags to be in english or to synonym to english will lock out a certain group of visitors who don't feel comfortable with english but would be a valueable addition to the community.
If we ever want to reach a level nearly as high as EL&U I suggest to use as much german as possible were appropriate and assist non-natives with tag-synonyms and an english interface. The localization should be complete as possible, maybe with a possibility for a user to choose his own interfacing but defaulting to german for new visitors, defaulting to english for SE users not located in the german region.
I've already invited 3 german teachers and one germanistic professor (with his main work about medieval german) and she + 2 teachers immmideatly backed off because off the english interface although they are as fluent in english as I am.
German and English and the English tags are synonymed to the German counterpart, so that the German versions are finally visible.
I guess subscribing to tags will work for synonymed tags too.
You can subscribe to tags on http://stackexchange.com/filters/ – if the tags here differ from other sites (like english) we make it unnecessary hard to detect the site and interesting questions.
Could the SX administration provide us with a new feature that simplifies the localization of tags? Something as simple as adding a translation field?
Honestly, I don’t care whether the tags are displayed in German or English, as long as they are synonymized correctly. Some tags are still only usable in English, because there is no German equivalent.
Right now, the process to make a tag accessible in German and English is to make sure the tag exists in both languages (create the missing one, if necessary), then make them synonyms.
This involves two tasks that require different amounts of reputation (150 vs 1250) as well as different levels of expertise (0 vs 5 overall positive votes in that tag). It is overly complicated, probably by design.
As long as no proper, 100% localization solution is present, I agree with using english-language tags and german synonyms.
Tag synonyms are possible, but I don't know who can set them up - I assume the moderator(s). I've started a separate question for collectiong synonym requests: Tag synonym requests
One base tag consisting english-german (e.g. cases-falle)
One synonym german -> english-german (e.g. cases)
One synonym english -> english-german (e.g. falle)
On the con:
- increased moderation amount
- slightly suffering readability of tags
On the pro:
- easy search (especially for native germans who are able to get additional hints about the question)
- easy typing - good keyword results.
And I guess we should poke the admin team for a) very good encoding (just noticed there is no html encoding meta-tag) and umlauts for tags. Falle is really misleading.