Just came across an article on Wikibooks about how difficult it is for native English speaker to learn specific languages.
Pretty interesting, thought the article has a ways to go to be fully developed.
From Article
This world is just full of hundreds of thousands of languages. Wikibooks also hosts many different language learning books, but on a smaller scale, of course.
Becoming fluent in a language is no walk in the park, even if you do already display an aptitude for languages. This Wikibook will act as a very useful guide showing how difficult learning any particular language you have set your eyes on is.
Many people wonder how long it will take them to become proficient in a certain language. This question, of course, is impossible to answer because a lot depends on a person's language learning ability, motivation, learning environment, intensity of instruction, and prior experience in learning foreign languages. Last, but not least, it depends on the level of proficiency the person wishes to attain.
The Foreign Service Institute (FSI) of the Department of State has compiled approximate learning expectations for a number of languages based on the length of time it takes to achieve Speaking 3: General Professional Proficiency in Speaking (S3) and Reading 3: General Professional Proficiency in Reading (R3). The list is limited to languages taught at the Foreign Service Institute, minus languages which don't have their own Wikibook.
It must be kept in mind that students at FSI are almost 40 years old, are native speakers of English and have a good aptitude for formal language study, plus knowledge of several other foreign languages. They study in small classes of no more than 6. Their schedule calls for 25 hours of class per week with 3-4 hours per day of directed self-study.