How to paste multiple strings into .net .resx files?

I have many .resx files used for translations in a large site. To get the translations done, I copy and paste the content of each resx file into a spreadsheet. The spreadsheet comes back from the translator with the new language appended as an extra column. I've tried copying the column from the spreadsheet and pasting into the value column in the resx file but it won't work. I'm now reduced to cutting and pasting thousands of individual phrases from the spreadsheet to the resx file. There must be a better way. Is there?