Since I use Google search in my website, I had a small problem with its results. Google normally checks your IP address, regional settings and cookies then return results in your language if its possible. In my case I got different languages in different browsers, when you create search profile in Google control panel, it does not provide any feature to set the search result language.
To solve this, when you search normally through Google website, look through the query string showing in your address bar, a parameter named hl holds language name of the result, if you change its value like this hl=fa you will receive search result in Persian, and en is for English.
For your website you need to add this inside Google search form for English language:
For other languages, at this time, Goggle supports these languages:
Persian=fa, Arabic=ar, English=en, Indonesian=id, Romanian=ro, Bulgarian=bg, Estonian=es, Italian=it, Russian=ru, Catalan=ca, Finnish=fi, Japanese=ja, Serbian=sr, Chinese (Simplified)=zh-CH, French=fr, Korean=ko, Slovak=sk, Chinese (Traditional)=zh-TW, German=de, Latvian=lv, Slovenian=sl, Croatian=hr, Greek=el, Lithuanian=lt, Spanish=es, Czech=cs, Hebrew=iw, Norwegian=no, Swedish=sv, Danish=da, Hungarian=hu, Polish=pl, Turkish=tr, Icelandic=is, Portuguese (Brazil)=pt-BR, Portuguese (Portugal)=pt-PT
Other Languages may be supported, if your language is not listed above you should check at Google website.