If you have a really popular website, the idea of expanding that site to reach more languages has probably crossed your mind. Such an expansion could mean a broader audience reach in more countries, higher traffic, and the potential for more revenue.
The latest webmaster help video, featuring Google's Developer Programs Tech Lead Maile Ohye, gives some great advice and best practices for expanding into additional languages and country-based language variations and ensuring your site is search-friendly.
Much of the video covers things like how you should approach a language expansion, things you should consider before doing it, and cases on how this can be done. It also touches on a couple of the more significant search issues that can impact a website regarding multiple languages.
One of the more important things to be sure you include on international variations of a website is the special language and regional tags that can help Google understand how they should be serving your websites and to what languages and countries. The use of rel="alternate" hreflang="x" is highly recommended to prevent many issues. Google has an entire help document on how to use these tags correctly and effectively.
One large potential search issue sites discover with language expansion are when sites the incorrect page is shown in the search results for the incorrect user. For example, this could mean showing the search results of the landing page URL of www.example.com/en-us/pretty-things when the user is searching Google from www.google.co.uk, when there is an en-uk version of that page available.
Another common issue is when the search results show similar URLs from your site, which confuses the user about which pages they should be going to, and why there are two different pages offered for seemingly the same site and content.
Lastly, search engines might not be aware of all the different languages and language variations that website make, or they omit some pages for different languages because Google doesn't recognize that the seemingly duplicate pages are actually serving a different audience or language variation.
The entire video is very detailed and lengthy. It is well worth watching if you're considering expansion into different countries and languages, so you can be aware of all these types of problems and how Google recommends you solve them to best serve your users.