Note: at the moment we are limited to using English on the site - if it anyone can construct a word white list for another language then we could look at extending the site’s function.
Some suggestions: the following are possible sources as they copyright free in most countries including UK and EU but not (but necessarily USA)
Dylan Thomas
Virginia Woolf
Earlier works by Jung in older translations. (Check specific case)
Many spiritual and sacred texts in older translations.
All original english language poetry other literature prior to C20th. (However care is needed if source is an edited edition -e.g. specific versions of Shakespeare might be problematic - Find an edition with authors deceased more than 70 years ago.)