How can I just change the language of Safari in iPhone iOS 9?
There is no way to override the language setting in Safari only.

There are multiple workarounds, though.

Google Chrome for iOS can help you translate web pages that are not in your language to something that is in your language. Google Chrome for iOS os a great browser for iOS.

To translate from any language to any language from any web browser use this(make sure to replace): https://translate.google.com/translate?&amp;u={URL GOES HERE}. Or, just go to this link.