Now that JLU has been updated to support non-ASCII characters in tags, we have the ability to introduce non-English versions of our tags, and use synonyms to match the Japanese and English versions together for people that aren't familiar with both words.
Should we? If so, to what extent?
The immediate benefit is with the particle tags. By having the particle written in Hiragana, we can help avoid issues where there may be two different ways to spell a particle in English, like with particle-e.
It can possibly help people learn terminology as they see their tag is a synonym of some word they've never seen before.
The site is now almost 18 months old, and we have been using English tags since the beginning. A switch now might be disruptive.
It may make the site harder to use for some people. Sure, there can be synonyms to pair the English tag with the Japanese one (or vice-versa, depending on what convention is decided), but that mostly helps when adding tags. Only the primary tag is shown on the question, not the user-entered synonym, so users browsing the question list may not understand or recognize the tags shown. (I'm not entirely sure about this, having used synonyms rarely.)
It may be harder for people to type non-English tags (this may or may not be an issue).
So, what do we as a community think? Would JLU benefit from the adoption of non-English tags? If so, would we use English or Japanese for the primary tag language?
I am all for having hiragana tags for common grammatical subjects such as こと、もの、と which are the kind of thing that bring new people to the site. (I am not technical but if it brings us up more in the search engines then it is also adding value to the site franchise as a whole.)
Personally I, like others, have seen little value in our tags. This would give us a facility rather like the indices in our text/reference books to help make use of past questions & answers.
In many of the other Stack Exchange language sites though, e.g. the French site, even if I don't know any French I can get a pretty good idea of what the tags mean, but with Japanese being a more distant language from English, I think it'd make browsing the site more difficult for someone who doesn't already know the words or have rikaichan or something installed.
I think it also might make things more difficult for some beginner users to locate and figure out which tags to use when asking a question.
I'm not sure of the specifics of how Stack Exchange does SEO with tags, but it might be a problem for SEO if the tags were in Japanese and people were primarily searching on Google in English.
Autocomplete when editing tags may not be possible with a Japanese IME and Kanji tags, though if people typed tags in English I think you could still get autocomplete for the tags using the English synonyms.
This is a minor issue, but the alphabetical browsing of tags is more difficult with Kanji in the tags page. Also in English you could type , and it'd automatically create a new tag when writing a new question, but when typing 、 with an IME you currently need to switch to English, type , then switch back to Japanese for the next tag which is a bit more work, though I think that's a fixable problem.
I think in an ideal world, if Stack Exchange was to implement localization officially and the tags were also localizable based on browser language/user preferences, tags would be displayed in English if the English localization was displayed, and Japanese if the Japanese localization was displayed, but I don't know how difficult that would be.