It's surprising how many conventions there are about writing numbers and quantities in different languages, and it's not always easy to know what approach to take when translating.

English-speaking countries tend to use a decimal point and separate thousands with commas. Most European countries do it the other way round. Sound of them, especially Franch, use a space to separate thousands, but not necessarily millions (and of course you need to use non-breaking spaces to make sure the number doesn't get split up at the end of a line).

So the usual approach when translating is to convert numbers according the language in question. But it's not easy to say whether these conventions are language-specific or country-specific. And there's a third possibility: that they are system-specific, meaning that even within one language there are times when you would use one system or another, or even mix them.

The metric system (more properly the SI or Système International) is associated with Europe and so a lot engineers are used to seeing the decimal comma used with metric units, but the decimal comma used with American units. As a result, some writers mix them when making conversions. So you might see

10.5 feet (3,20 metres), or
1,48 bar (21.46 psi)

This works quite well in tables, but can be confusing in prose, especially when some of the numbers have no units.

The ISO (International Organization for Standardization) and CEN (Comité Européen de Normalisation) both specify that "the decimal sign shall be a comma", whatever the language, so they would write 3,20 m and 1,48 bar. (PDF)

American companies in particular, when planning to translate technical documents into European languages, have to choose between a number of options, including whether to convert to metric and, if so, whether to use both systems and in which order, etc. A source text containing "10.5 feet long" might end up in the target text with any of the following:

And what about "ft" anyway? Is it a symbol, not to be translated? An abbreviated word, to be translated? Should it have a dot after it? A space before it? That's for another day.
 

For more entries on Formatting, click here.

For more entries on Numbers, click here.