18:02 Jan 18, 2010 

It is not entirely simple!

The Concise Oxford and Oxford Advanced Learner’s dictionaries give socio-economic with a hyphen as does John Adam: Dictionary of Business English (Longman), while the Longman Dictionary of Contemporary English writes socioeconomic as a single word like Webster, as one would expect in the US.

Maybe my age is showing, but I still prefer to use a hyphen, because the second element begins with a vowel. However, I would unhesitatingly write sociocultural, sociolinguistic (supported by the Oxford dictionaries...)
If you feel that is illogical, then you are entirely justified in writing socioeconomic as a single word.

I would check the rest of the text for clues and if possible other material from the same client or their website to see if they showed any preference.
As a tentative guide, US writers are more likely to avoid hyphens, either writing separate words or a single compound word without a hyphen, but here you are probably writing for a UK target group. So it is actually up to you!

I will leave it to the Danish specialists to suggest a good translation.