Hi Jeff,
as you point out, translating content generated by users is a very different task that translating the fixed strings in the product.
In this case, I would recommend to extract contents via Liferay API. A simple custom development can export all the contents in the source language into a set of files which could be imported as source translations. An issue you should address is the mapping of exported contents and your translation system entries. A possibility is to use the pair articleId, groupId during export. A more user firendly way is to use title,groupid, but title is mutable whilst articleId is not.
For the other way round, Liferay API can be used to update the contents with new translations exported from your translation system. Just make sure you are able to map exported data to existing web contents (I'm assuming that you can't create new content from translation tool, so that all exported content should pre-exist in Liferay CMS). For deleted contents, just make sure that your Liferay2translationtool code deletes anything in the translation tool which don't exist in Liferay, just to keep them in sync.
Hope this helps
Regards,
Daniel.
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