Rule-based translation : adjective accordance : interesting stuff:
sur les réseaux japonais et américain (fr) = annantu à e rete sgiappunesa è americana (co) = on the japanese and american networks (en)
noun (networks) is plural but adjectives (japanese and american) are singular

The excerpt refers to the ‘single) japanese network and the (single) american network
I guess (to be confirmed?) that the following sentence is ambiguous in english:
‘the japanese and american networks’: are there one or several japanese network(s)?
are there one or several american network(s)?