After reading some articles I figured out that some elements in wikipedia shows a strange loading behaviour:
The navigation is is showing a "navigation"-button above "Main page" until the site finished loading, then the button disappears. The menu entries aren't expandable while the site is loading, all menu entries are shown. This might be due to wikipedia's custom theme (not logged in btw) or something and makes the loading experience really inconsistent. Possible fix: Menu-entries like "Navigation" shouldn't even appear when disabled.
Further there is an issue with the Tigrinya and arabic language font. If you read (look at) articles containing rhe Tigrinya language (for example https://de.wikipedia.org/wiki/Eritrea and https://ti.wikipedia.org/wiki/%E1%8A%A4%E1%88%AD%E1%89%B5%E1%88%AB ) it seems like the site is loading a thinner font, then the font is disappearing and a bigger font appears. Surprisingly this issue doesn't appear [on one article?] in the english wikipedia: https://en.wikipedia.org/wiki/Eritrea
The font-reloading also happens to the arabic language, see the same articles above.
Furthermore there is an issue in ti.wikipedia.org: untranslated english text like "Log in", "create account" etc. is not using wikipedias default font but apparently the (ugly) latin letters from the ti-font.
This issue can be reproduced in Firefox, Internet Explorer and Chrome.