Is it appropriate to ask an author for an English translation of a paper? I have found an interesting paper which is very relevant to my research. After reading the abstract in English, I would like to continue to read through the methodology and its discussions. However, only the abstract is available in English, and the content is in another language which I don't know.

I really want to read through the content as some of the figures are very interesting to me. I have tried to translate it using Google Translate, but it is very difficult to understand. 

Is it appropriate to send a polite email to the author, asking for a translation of your paper in English? Does the author have the obligation to do so?
As far as I'm aware there is no obligation to provide a translation of a published paper from one language to another. 

I think it would be rude to ask for a translation of a paper. However, it would generally be fine to enquire as to whether such a translation exists, or whether similar work has been published in English.

More broadly, it may be in the author's interests to provide an English translation in order to increase the impact of his or her work. 
If the work is really important to you, you could always pay for a translation. At the extreme end, perhaps where there are a large number of important works in a particular language, you may even want to learn the language.