Change the language in the preferences for Apps in the CC desktop application and install an Arabic version again.
InDesign will always use the language of the OS if it is installed, but when the Arabic version is added you will find more commands which allow you to create and edit RTL documents in Arabic.
For correct document not the User Inteface language is important, the language and fucntionality of text styles and document is important.
Thank you for your answer! I have now finally managed to get the right language in to my InDesign and there are more options. But the problem is still there. And the same as when I worked in the Swedish version. When I do copy paste from the translators pdf (worked in Word and then saved to pdf) I still get small extra caracters in the text. I use Times New Roman - same as the translator. Like this: