The past tense is silent with respect to whether the past assertion is now true. There is no implication that it is or may be no longer valid. "I suggested that the word zeitgeist was of German origin" is simply a statement of what was suggested, without reference to the present. You do not have to change was to is if your intention is to recount or relate what you had suggested.
This is a comment to a question done by MrTROMANO I just would like to know why he used "had suggested" , why did he use past perfect , seems strange as in the other sentence he used past simple , is it to emphasize the suggestion or does it mean you had suggested before you asked the question