Translators who Volunteer vs. Volunteers who Translate
A professional translator writes something that does seem to be translated, it seems that it was written in the original language. The professional can follow instructions about how he/she should translate, about the tone of the translation, about style, etc.
The work received from volunteers usually has low quality, is not according to glossary, and needs to be corrected for minimum quality. You cannot ask for deadlines or complain about quality from volunteers. Volunteers do not how to solve difficult situations (the text does not fit, etc.).
Volunteers do not understand tools like glossary or instructions (what should be translated or not), etc. Volunteers would need different sets of instructions, of a lower level, to be able to follow (make sure you spell-check).
Tutoring of volunteers seems the way to go, but professionals usually do not like it, but it works when the professionals are paid to do it.
What can be taught to volunteers that would help to raise the quality of their work? It would be good to teach them before they are allowed to start being volunteers. It has to be limited because it is not a core activity in their life.
A crash course on translation should be included in the Book.
Not word by word Read the sentence and make sense of it before you attempt to translate. Use glossary Etc...
The TED.com experiment, where volunteers (1,200 at the moment) translate videos that they choose (an probably are passionate about), tutored by other volunteers, is an interesting experiment that might give new information on how to work effectively with translators.