Looking at lorem ipsum is all very well, but the real test for a font is how it works on real pages. The following sites (except unicode.org and wikipedia) are news sites. This page is not maintained and some links, particularly from the BBC, might have disappeared following political pressure for reduced costs.
The BBC pages with news in different languages are at http://www.bbc.co.uk/ws/languages
When last checked there were fewer pages than there used to be, and all of the African pages seemed to use a vanilla latin alphabet without any accents or extra letters. But the following pages, if still present, may be useful for testing fonts: Arabic, Azerbaijani, Bengali, Burmese, Chinese (Simplified), Hindi, Japanese, Kyrgyz, Pashto, Persian, (Brazilian) Portuguese, Russian, Scots Gaelic, Sinhala, (Latin American) Spanish, Tamil, Turkish, Ukrainian, Urdu, Uzbek, Vietnamese, Welsh.
And of course there is http://news.google.com where other languages can be accessed from the 'cog' settings icon. When checked in 2016 these included: Arabic, Brazilian Portuguese, Bengali (Bangladesh, in Devanagari), Bulgarian, Cantonese (Traditional), (Mandarin) Chinese (Simplified), (Mandarin) Chinese (Traditional), Czech, Dutch, Flemish, French, German, Greek, Hindi, Hungarian, Indonesian, Israeli, Italian, Japanese, Korean, Latvian, Lithuanian, Malayalam, Norwegian, Polish, Portuguese, Romanian, Russian, Serbian, Slovakian, Slovenian, Spanish, Swedish, Tamil, Telugu, Thai, Turkish, Ukrainian, Vietnamese.
Also, there are (more) examples of Article 1 of the UDHR at http://unicode.org/udhr and there are many language-related pages at wikipedia - many languages have their own wikipedias.