Can you explain to me the difference between the two words? Is "controller" always the chief of accounting department and accountant more of a general word for somebody who manages company´s finances (together with other accountants?)?
Yes, that's pretty much correct. Usually a financial controller or financial director oversees the financial sector of a business or group. Accountants work under the controller and do the day-to-day tasks.
In accounting the word "controller" has a special meaning, which is "control" of accounts themselves, which is to say, to keep them correct. This would, nevertheless, tend to mean overseeing the work of others in this respect, so a controller is likely to be quite senior. However, it may not necessarily imply that they are the most senior, in fact some "accounts controllers" may be assistant accountants. In other words, you cannot be sure that someone with the title "accounts controller" is senior management.
The word can be qualified, for example, according to the department or type of accounts "controlled" (e.g. a credit controller, controller general).
An accounts controller is sometimes called a "comptroller". Someone with this particular title is very likely to be a senior official.