Redmine

I might be wrong here, but I think for any decimal form of a number, the unit should be written as a plural. Singular form with numbers applies--I think--exclusively to whole integers.

Even 1.0 would use "hours". At least, "one point zero hours" sounds more correct than "one point zero hour".

English:
Decimals below 1 are often folled directly by plural nouns. [..] Fractions an decimals over 1 are normally followd by plural nouns.
Source: Practical English Usage, 3rd Edition. Section 389.2. See also 532.9

German: like english.
http://www.grammatikfragen.de/showthread.php?190-Ist-die-Zahl-0-5-Plural-oder-Singular

French: A bit different.
http://www.druide.com/enquetes/15-gramme-ou-15-grammes
http://fr.wikipedia.org/wiki/Wikip%C3%A9dia:Conventions_concernant_les_nombres#Accord_du_pluriel

Spanish: like english.
http://buscon.rae.es/dpd/?key=n%C3%BAmeros&origen=REDPD Section 1.2 b.
http://www.fundeu.es/consulta/1-0-litro-o-litros-concordancia-25138/

Attention:
It's "1 hour", but "1.0 hours". Or in german "1 Stunde", but "1.0 Stunden".

Could someone confirm the grammer rules for french or spanish language? How are the rules in other languages?

Grammar rules for spanish are okay.