I have a international webservice (6 languages) with about 1000 people daily who access from any device, from smartphones to internet-cafes.
The information displayed are a bit scientific, for example distances, amounts, and dates, and the format can affect the decimal separator and the understanding of values.
1.000,000 (German) is correct, sometimes
1,000.000 (English) is correct.
I should allow different formats, but what should happen if the user inputs
1.000 (one thousand in German formatting but one in English formatting)?
Unfortunately 'Don't Make Me Think' does not write a lot about formatting; the only thing suggested is to leave formulae blank to keep the company from wrong inputs.
Question: should I rely on the formatting of their device or should I let the user choose the format themselves?