tl;dr: Some languages are written from right to left; you must use the correct writing direction for each language.
Most commonly, languages are written from left to right like English, but some languages, such as Arabic, are written from right to left. In order to keep translated text readable, your presentation needs to address the writing direction issue. In HTML-layouts, just specify dir="auto" attribute to text elements and the writing direction will be correct - see the example below:
English is written from left to right:
Coming soon in Arabic!Arabic is written from right to left:
قريبا باللغة العربية!
As you may notice, the line is also flipped to the right. The user interface in general should be mirrored to the right, as the native speaker of RTL-language will look at elements from right to left.