The English has two spaces for a new sentence here (which is fairly normal). Does the Dutch consistently only have one? If not, I'd rather things were left alone until a decision is taken on which form to follow.

In Dutch, full stops are consistently followed by a single space. Using double spaces would look weird. There was a time (the age of typewriters), that double spaces after full stops were common in Dutch typewriting (like for English and other languages at the time) because a single monospaced typewriter space was not sufficient to show the larger inter-sentence space (the em-quad) that was commonly used in traditional typesetting of books. However, especially in Dutch it mostly disappeared after the dawn of computers.

Interestingly, in French it is common to have spaces precede exclamation points, question marks, colons, and semi-colons. For instance:

 187         <source>Personal Mix at: </source>¶
 188         <translation>Mixage personnel à : </translation>¶

2859         <source>Do you want to open the ASIO driver setups?</source>¶
2860         <translation>Voulez-vous ouvrir les configurations des pilotes ASIO ?</translation>¶

English has two spaces for a new sentence here (which is fairly normal)

That never occurred to me! :-) I'd assumed we were using singles on Jamulus... I'm pretty sure we are?

Interestingly, in French it is common to have spaces precede exclamation points, question marks, colons, and semi-colons.

Not only "common" but "obligatory" since given by the French writing rules (note: optional for the semi-colons).

Not only "common" but "obligatory"

And, being French, the punishments are probably quite severe ;)...

Probably something very hard like... an English typographic writing lesson ;)