In response to your question I would strongly advise you don't mix languages because this would have several effects to your SEO efforts:
1) Dilution of country relevance - if your primary target country is UK and you have Indian content then this isn't relevant. Google and other search engines therefore won't see your site as focused to your target country audience.
2) Poor user experience - From a user point of view they expect to see English content when selecting the English language selection. As a result the search engines like Google won't reward you as strongly because you could be seen as misleading users and providing a poor UX.
1) Ensure that you use a universal TLD (e.g. domain.com) and then annex your content via sub-folders for different language translations (e.g. domain.com/in/ ). Your primary language can be English on the main .com version and other versions can provide alternative languages.
2) Use Lang tags for different translated content. This also tells Google and the other search engines which country search engine you want that content to be ranked on. i.e. GB would be Google.co.uk, IN tag would be India etc.
3) Use Google Webmaster Tools Search Console to verify different language site areas as individual websites in Google and Bing Webmaster Tools. Then in the country setting assign the appropriate country for that sub-domain.
I hope that makes sense and helps. If you require any help to do this and advice, we are always able to provide consultancy services for SEO at great prices. Please contact me on rstoubos(at)odysseynewmedia(dot)com for more help.
Owner of Odyssey New Media Ltd