This article is written in British English, which has its own spelling conventions (colour, travelled, centre, realise, defence, artefact), and some terms that are used in it may be different or absent from other varieties of English. According to the relevant style guide, this should not be changed without broad consensus.
I'm no linguist but I think the name should be Postjager, because AFAIK Dutch doesn't do umlauts. Jäger is the German, not Dutch word for hunter. Wesselink and Postma's book, De Nederlandse Vliegtuigen, spells it postjager and they should know. For now I'll add this as a redirect.TSRL (talk) 20:49, 18 February 2013 (UTC)
Seeing this comment has been uncontested for 1½ years, and totally agreeing it, I will rename the article. Jan olieslagers (talk) 13:28, 19 August 2014 (UTC)
Except you also removed the hyphen, when pretty much every source (including Dutch, English and French) I have uses either a hyphen or a period between the S and the 4. (no umlauts to be seen anywhere though) NiD.29 (talk) 09:59, 22 August 2014 (UTC)