Language settings

Set the language on the device to English and launch this test case
If the device has more languages available set another language and launch this test case
Repeat Step 2 until all the languages available on the device are tested

Accept-Language:
Current window.navigator.language is:

Expected results:

Step 1: Current "window.navigator.language" is en, or en-GB, or en-US or other valid shortcode for English. "Accept-Language:" header contains English shortcode as the first language. Rest of the languages which can be presented properly on the device using the current setup are listed after it.
Step 2: Current "window.navigator.language" is a valid shortcode for language currently set on the device. "Accept-Language:" header contains the current language shortcode as the first language. English is listed as the second one. Rest of the languages which can be presented properly on the device using the current setup are listed after it.
Step 1&2: Look at the 3 symbols tables below. Depending on language of device / language configuration on the device, same symbols from unicode block must be displayed as images above. Symbols shown in Latin-1 Supplement sections must be always shown properly (this unicode block contains for ex. Copyright symbol)

Unicode block:

Latin basic

Latin 1 Supplemenet

Latin Extended A

Reference image of symbol: