I am a Nigerian but I applied for UK Adsense account on my website (amnaijanews.com) with English language content on it, in few days, they review my site and disapproved my application for the reason listed below:

Your AdSense application status

As mentioned in our welcome email, we conduct a second review of your AdSense application once AdSense code is placed on your site(s). As a result of this review, we have disapproved your account for the following violation(s):
We did not approve your application for the reasons listed below:

Unsupported Language: We've found that the majority of your site’s content is in a language that we do not currently support. Right now, we're only able to offer language support and ad targeting for the languages listed in this help article. If you manage or own another site in one of our supported languages, feel free to resubmit your application as described below. While we look forward to supporting your language, we don't yet have a date as to when AdSense will be available for you. If you'd like to stay up-to-date with the languages that we support, please feel free to check back with us at the above link.

Please, i did not understand Unsupported Language they mentioned.