This community occasionally receives "how do you say" requests -- requests to translate a specific word or phrase into a given language, a list of languages, or any and all languages.
While such requests are expressly allowed, it's true that there are some words and phrases that are especially popular (such as "Merry Christmas and a Happy New Year" and "Happy Birthday"). Accordingly, there are multiple websites out there that collect translations of such words and phrases.
Unfortunately, the quality of such sites varies; in particular, many of them tend to transliterate everything to the Roman alphabet and to strip some or all "unusual" diacritics that are needed for writing some languages. This makes googling for translations a hit-or-miss thing if you can't evaluate the quality of the sites you get in the search results. Seeing the same translation on multiple sites isn't always a point in favour of that translation being correct, as some sites seem to copy from one another, so mistakes simply travel from one to another.
However, the Omniglot phrases at http://www.omniglot.com/language/phrases/ seem to be good, in that they use the native script (with Romanisation in addition to, rather than instead of, the native script), and the quality of the translations is reportedly good, too. Apparently, the maintainer is also responsive to requests for additions or corrections.
If you know of other good sites, please let the maintainers know at the email address listed on the community's profile.
(I've also heard of http://www.freelang.net/expressions/index.html; if someone can evaluate the quality of some of those translations, please let us know, too. That site has native script for some, but not all, languages using non-Roman scripts.)
Also, please use the tag "howdoyousay" on new "how do you say" entries (in addition to a language-specific tag if you're asking for translation into a specific language); this will let users find such entries by searching for entries with that tag, so they can determine before posting a request whether that word or phrase has been requested in the past.