Is it OK to publish a book as an undergraduate?
Go for it, and see whether you can get one of your professors to do a technical review. That technical review, acknowledged in the preface, will lend weight to your book. If you have professors who speak your language, think about co-authors.
Do not, however, expect to make money. Only blockbuster textbooks make significant money for their authors. Also, beware vanity publishing, where you pay the publisher rather than the reverse.
If you write the book, Amazon will let you make it available free or very cheap. (That's true for English language books; you'll need to check about other languages.)
IMHO, it doesn't matter whether you are an undergrad or a professor when it comes to writing books; what matters is whether the material you would like to share has some value for readers. If you strongly and rationally believe in your book idea, approach book publishers with a comprehensive book proposal.
Some considerations:
Objective Be clear about the motivation and objective behind writing the book. Do you want to share knowledge in a systematic manner and/or you want to make money. Be aware that books will not earn you a lot of money unless it becomes a blockbuster.
Time/Effort Book writing is a long and demanding process. Do you have sufficient time to work on it (considering you are a student presently)?
Skills Assess your skills. Assuming you know technical stuff, can you express your thoughts decently in words. If you are writing, for example, blogs that are received well by your target audience, you should be fine.
Market research Carry out some market research. Try to state in words what your book will provide which is not really provided by the existing books.
Other answers have touched upon this a bit, but I think it matters greatly whether you self-publish or not. If you can get your book published by a reputable press, then it will surely help you. If you self-publish then it could hurt you by making you seem naive about academic publishing and making you seem overly egotistical if the book isn’t high quality. Whether this will be the perception will depend a lot on whether there is original content and if that original content is seen as having value — but if you can’t get published by a reputable publisher the assumption will (rightly or wrongly) likely be that the book lacks such value. If there is original research that is publishable, but maybe not a whole book’s worth, you might be better served by submitting an article to a journal/conference.
However, it sounds like your main motive is to make existing material available to audiences who speak a different language. If that is the case then being fairly conservative with what you write, making it more a textbook than a research manuscript, can help you (assuming it’s done reasonably well). What I would do in such a situation is to list it in your CV under “service to the profession”. This will avoid giving the impression that you take it to be serious original research (assuming it isn’t), and show that you care about making the relevant knowledge more easily accessible to speakers of the relevant language. In such a case, though, it might also make sense to simply produce a translation of the sort of work you think is lacking (with permission of the author and publisher, of course).