Sometimes your client does not have the files that will be translated, but he still has a deadline that cannot be postponed and needs to know the translation price and if you will be able to deliver the files on time.
In other cases, the client is just quoting a project to his client, that might or might not be approved. So the files were not created yet, but he still needs to know the price and time spent on translation to include it in his quote.
Yeah, I know, they are the worst case scenarios. You cannot promise anything to your client if you do not have the files. But with no price and deadline, he cannot get his client approval and will not create the files.
If you include a big buffer to your deadline and/or price, probably you will not be able to get it approved. If you give a low price and a short deadline, maybe the files will be worst than what you thought and you will have a loss on this project.
I usually receive that kind of request, so here are my tips:
I ask everything that I can get from the client. Number of files, pages, any sample material, maybe a similar material they already produced etc
If I worked with that client before, I will try to follow the same kind of project. For example: if the client knows he has a 20 pages documentation and I already translated a 30 pages documentation for him, I will try to be guided by this last project.
It is still better when I have plenty of past projects, so I can get all the previous information to estimate the actual quote.
Every possible place I always gonna say it is an estimative. "I am estimating X pages to DTP, Y words to be translated.".
Whenever it is possible, I do not send an official quote but, instead, I use separate values in an e-mail message. So it is easier to the client understand it is just an estimative and not an actual quote.
I ALWAYS use conditionals. To achieve this price or that deadline, I am gonna need these requirements here. "If the document has 2000 words", "If we receive the files by tomorrow noon", "If the number of graphics to be edited is up to 15".
This will make sure the client will not promise me a 20 pages DOC file and send me an 85 pages PDF file with only images. The conditionals are there so if anything comes out of hand, I can come back on them and renegotiate the price and/or deadline.
The client is not your enemy. You are working together, so if the material is easier than you estimated, adjust that quote. You are going to get more projects when people trust you.