Does having multilingual content help SEO in a given language?
Does translating English articles into Spanish and French improve the rankings of the English content? No.
Over time, there could be positive spillover effects if you build a brand and gain backlinks in the other languages.
Short-term, you only add complexity and need to get Google to crawl and index x-times as much content as before.
Is this generally a good idea?
- You will spend x% of time translating content which will either slow down content production or make content production more expensive.
- You will need to set your website up for handling multiple languages, which adds complexity to templates, UX design, UI design, and internal linking logic.
- You might have to set-up and maintain hreflang to avoid the wrong language-version ranking in some countries.
- For maximum impact, you must promote your website/brand/content in every language and build links in every language.
- If your content is unique and there is already demand for it in other languages, this can be a low-hanging fruit.
- In some smaller languages (like Finnish) there is less demand. But also less competition. You might have it much easier to rank well.
How should I determine what language to direct users to?
If you mean redirecting users, don't! Language/country redirects are one of the worst UX crimes a website can commit. Make it easy to switch the language version and potentially even suggest the most fitting one. But never redirect users - unless they have previously indicated a preference to always see your website in a certain language. Forced language/country redirects cause a lot of frustration!