This is not a simple question to answer, and particularly not without additional context.
I am presuming you are talking about non-English words inserted into English language text. That can be done, but is generally fiddly until you figure out how to come up with something that's a pronounceable substitute for the word that sounds right with the synthesizer you're using. I am guessing we're talking about words from non-romance-languages.
A short list of examples, and knowing what synthesizer you're using, would be most helpful.
Brian - Windows 10 Pro, 64-Bit, Version 1809, Build 17763
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