So that’s what happens when a site decides to join the tagging fever:
Tags: php, dd, tutorial, shiflet, shiflett, zend, framework, web, site, anirudha, fdffffffffffffff, hello world, httpwwwgooglecom, kjkljlkj, asasas, vinod, chilli, shiflettasshat, mama, papa, chuckoo, sathishan, nithyan, ashokan, unni, divya, pradeep, abcphp, zde, jayesh jose, harro, ronnie, sample, oui, lebicheur, controller, error, d, kontrola, omg lol, 5, 46457, dfsdfdsf, sdfsdf, asd, crazy, booga, should tags be allowed to be added like this, no i dont think so the tags should be extracted from content, dont allow users to add tags or youll see the results, tags are the root of all evil, thi is, cvcxv, ioncube, zend framework, you already see the results, has not printable version, user created tags how lame, pet the monkey, shoutmouthcom, maybe only registered users should be able to add tags, adding another worthless tag to hammer in the points made earlier, this is only way to add new tag, didip is a complete bonehead, rapdwordpresscom, trke olmayan dkman, turkce olmayan dokumanlar, prova
I have mixed feelings about tags, but in this case, tags seem pretty much useless.
Two years ago I was an absolute tagging enthusiast, but I have slowly moved towards a more cautious opinion. It’s like wikis: if there’s not someone exercising some quality control, the content gets easily polluted when the number of users grows.
Even though, I still believe that their flexibility is also their advantage over other ways of organising information. But unless you use these methodologies in a closed, controlled environment, things will screw up pretty soon, I guess.
You just need to take a look at del.icio.us or flickr, two of the most famous tagging-enabled sites. There can be several tags in different languages for tagging the same thing. Or maybe somebody will prefer to separate multi-word tags with underscores, whereas other prefer points. Or hyphens.
The syntactic problem is slightly irrelevant, but the semantic one is not. And I’m not even going to enter the issue about mechanical tags, vandalized content tagged with really wrong tags and all that crazy stuff!
Oh and if you feel curious, this is where I found those absurd tags.

HappyWebCoder
I agree 100% if you are talking about collective tagging, where any user can (un)tag a content for everybody: almost every collective interaction needs supervision if you want people to follow some rules. We have digital examples on forums and, as you said, grupal tagging and wikis.
When it comes to individual tagging I can’t see any problem, actually I found it a cool way to organize information – if you are able to respect your own tagging rules, of course! ;)
As Sartre said, ‘Hell is other people’
Rami Kayyali
Actually, I find tags useful even with the proliferation of mess. If anything, it connects like-minded people together. Those who use similar, messed-up tags are more likely to be in the same social group.
The taxonomist in me struggled for a while when I moved my bookmarks to del.icio.us, but then I found how useful tags are. e.g. I can find all the programming frameworks I know by visiting del.icio.us/rami/frameworks, and filter that down to PHP with del.icio.us/rami/php+frameworks. I like that.
One idea to somehow fix the problem you mention is by allowing people to define tag synonyms. It could happen over time in the context of the application itself. Say you’re browsing certain photos tagged with “fotografías”, you can click on, say, “Add Synonym” and enter “photographs”. Collectively, we’d end up with tag synonym groups, which would make searching much easier.
HappyWebCoder
@Rami: synonyms could be dangerous with polysemic tags, which could be frequent on the multilingual context that you describe. That’s why I always use english tags ;)
sole
@Rami – I like the idea of tag synonyms. But I have the feeling that they should be moderated by editors somehow.
Although of course they could be dangerous when you put two languages side by side and try to find funny things.
Rami Kayyali
I know it becomes difficult to manage synonyms in a multi-lingual context, but that’s an extreme. If we stick to English tags, we can also define synonyms and semantically-related tags, like fotos, photos, photographs (for the Americans, the English, and the Nitpickers).
But why moderated? Isn’t it chaos that makes tags useful?
sole
Ah, I was thinking of moderated just for avoiding vandalism. But I was also assuming a very large amount of users, of lots of different countries and languages.
Normally the chaos only appears in that situation…