Most of us encounter languages other than English when we are doing our ancestral research. For those brave enough to tackle translating these documents, I would highly recommend a series of books called "In Their Words - A Genealogist's Translation Guide to Polish, German, Latin, and Russian Documents".
These guides were created for Polish genealogy research, but of course, the language guides can be applied for other areas of the world as well. Poland did not exist for well over 100 years and during this time it was split up into areas known as Prussian, Russian, and Galicja (Austrian). Languages from each of these countries became the language used in legal documentation, so eventually you will encounter those languages for the specific area of Poland your ancestors lived in. Latin is found in the Catholic Church in many countries in the world, so this language guide can be used by many people doing research. Polish will be useful for Polish research. Russian translation guides will be perfect for any of the areas that Russia occupied over the years and the German guide for Germany.
This incomplete series is being written by two language specialists Jonathan D. Shea & William F Hoffman, Published by Language and Lineage Press. Out of the four books to the series, three have been completed. The first three volumes are - Volume I: Polish, Volume II: Russian & Volume III: Latin. The fourth volume (German) is being worked on, and I know there is great expectation for its release, although the exact date is not yet known. Each volume ranges from about 375 to 500 pages. Each guide includes numerous examples of documents and extracts from multiple sources, analyzed and translated. Examples include extracts from birth, death, and marriage records of various formats; gazetteer entries; revision lists; obituaries; population registers; military service records; passports; etc.. There are sections on grammar, phonetics, and spelling. They also include information on how to locate records in America and Europe, including contact information for various archives in Poland and neighboring countries. There are chapters on gazetteers and how to use them, with maps showing Poland's changing borders and administrative subdivisions. The vocabulary lists have thousands of words, especially those words most likely to be found in records, including many overlooked by most dictionaries. These guides are so popular that the Russian guide has already had to go to press a second time.
I HIGHLY recommend that you included these books in your research library. I see them as an absolute neccessity for extracting information out of records written in foreign languages. Get up your copy here.