Did you know you can get more audience if you write in their own language? You may have a higher bounce rate if you do not offer the page in their native language. If you don’t know the language it may be the time to get professional translations.
You should consider translating your website or blog if you have at least 25% of you traffic from those language speakers. It will be much easier to retain them and make them part of your loyal audience.
Also be sure you are not overdoing it. If you have a review blog with half of the readers from USA and the other half from Canada, translating reviews for products that are available in Canada into French is usually a good idea. But if a deeper analysis tells you that only 10% or 15% of Canadian readers are using the search engine in French maybe you should only translate the important pages of the blog and encourage your French readers to use machine translation.
Machine translation is a wonderful tool but it can produce inaccuracies so resist the urge to use for translating important information on your website or blog and use human, professional translations.