I am a licensed IP attorney with over a dozen years of experience. It is a pleasure to assist you today. I will answer your questions in the order in which they appear.
If I use someones language from their website, a book, etc and give them credit by providing source on my website, am I violating copyright law?
No...at least not technically as long as you reference them correctly and in the web context, link to their sites as well. That said, there are some cases in which injunctions against this activity have been granted when express permission (license or assignment) has not also been secured when you are arguably making a profit off of the information that you are referencing.
That leads to your second question, which is a good one as well.
Also, is there a difference between what I just asked above and if I do the same thing from a non for profit site, wikipedia, etc?
The profit component makes all the difference in the world relative to injunctions being issued against use. If you are a non-profit, and you properly cite/link, etc., it is very hard for entities to mount any sort of legitimate legal assault against you. This is because of things like the Fair Use Doctrine and other equitable arguments.
If you are making a profit, however, as mentioned above, you do run the risk of being shut down by courts that can be persuaded that you are being unjustly enriched based on the information of another entity, to which you are not paying any sort of license or royalty and without permission.
In short, the best laid plan is to seek written permission if you are profiting off of their information.
Let me know if you have any other questions or comments.
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Best wishes going forward!