.net multilingual sites

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.NET

multi-lingual

I have a .NET webforms site and a .NET MVC site. I want to make them multilingual.
This is not a "how to" question. I want to know, high level, what people have implemented in production sites and the pros and cons of those implementations.
How long did it take to implement?
How difficult is it to modify verbiage or other parts of the site?
Did you use a CMS or other third-party tools?
Did you use any automatic translations?
Do you have any other advice?

What I have tried:

Using resource files. (Note: I had to put something here.)