cannot input vietnamese words

sometimes I can type in vietnamese words to find its meaning, but most times it would not allow me to do that. What am I doing wrong. I want to be able to type in vietnamese words with its accent marks and find its meanings all the time. And if the word is not there I would like to add it to my personal dictionary, but it would not recognize the vietnamese fonts so as to add it to my dictionary.
The reply is "one of more of the words are not vietnamese text"

Have you seen this problem before and how was it resolved?

Hi,

Please let me know the full name and version number of the software you are talking about as well as your device model. Thanks.