There's no way you can decide whether a word is English, German,
French, Italian, or whatever other language based on the word
alone. Think about it - if it was that simple, there wouldn't
be reason to markup the words to aid the speech sofware - the
software would already know.
in reply to detecting the language of a word?
You can't use a simple lookup in a database, there are words
in English that exists in other language as well - which sometimes
a totally different meaning. If you are going to automate this
(and this isn't an easy task, people have been working on this for
decades), you will have to look at the context. You will have to parse
the sentences, and actually understand each word. And even then
you might have problems with sentences like 'time flies like an arrow'.
I suggest that you research the literature on computarized linguistics,
automatic translations, and speech software.