to the URL of the page and press Enter. Replace LANGUAGE_CODE with the code of the language: en for English, fr for French, de for German, ru for Russian, es for Spanish. Here's a list of other language codes.
Google usually tries to detect your language, but sometimes it makes mistakes. A few months ago, I visited Gmail's help center and all the text from the page was in Russian. Fortunately, there's a drop-down that lets you change your language at the bottom of the page, but not all Google services offer this feature.
For some reason, the "hl" parameter doesn't change the interface language in Gmail and Google Drive, while YouTube shows a link that lets you change the language.
This trick only changes the language of the Google page you've opened. To permanently change the language used by Google services, check this page. Services like Gmail, Google Calendar and Google Drive let you change the language in the settings.