Reference for use of Hebrew in public and private devotional speech

Can anyone provide a halakhic reference, from the Tanakh, Oral Torah, or otherwise, as to why blessings are always said in Hebrew, as opposed to German, Latin, English, or any other language that the congregation or individual Jew speaks?

I can understand why the Tanakh is recited in Hebrew; that was its original form, after all, and it may be said to lose something in the translation (though I maintain that Latin has a certain level of… erm…. gravitas). Then again, there are actual halakhic requirements for Torah scrolls, even the Aron Kodesh/Holy Ark.

Something like Friday night kiddush, though… well, the justification there becomes thinner and thinner. Can anyone point to actual sources for why Hebrew must be used for that blessing? Or even for the Sh’ma, when given orally? The Ashamnu might easily be pretzelled into the Peccavi, and so on.