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Had not to experience these issues with languages. Did you already set up master language and fall-back languages?
http://webhelp.episerver.com/latest/en/platform/multiple-languages.htm
Just a thought: if you are managing 10+ languages on the website, it will be hard to manage through resource files. You can write your own LocalizationProvider to manage translations in Episerver cms. (There are add-ons available as well. )
I have noticed multiple issues when using Projects and I try to update an existing page. I make the update in english but then need to duplicate the english to my other languages in order to export the project for translations. When I duplicate it, it doesn't duplicate over what is already in the file (requiring me to do it a couple times), then it doesn't always automatically place the language file in the Project folder even though I am already in it. This requires an added amount of time to double check everything across 10+ languages. I am able to export the files. Then sometimes when I go back in to the project to upload the translation files, all the original language files are missing in the Project and it basically requires me to manually copy/paste all the changes I had for each page/language.
Has anyone else experienced this problem? What is your workflow for making an update to an existing page. Maybe I am missing a step? Thanks!