-Merge: documentation updates from 1.3 branch


git-svn-id: http://svn.openttd.org/trunk@26137 6aa0318a-3be1-0310-93fa-89fd2396df07
-Fix [FS#5821] (r26105-ish): [Script] scripts could trigger the internal IsValidRoadType assertion


git-svn-id: http://svn.openttd.org/trunk@26138 6aa0318a-3be1-0310-93fa-89fd2396df07
-Update from WebTranslator v3.0:
latvian - 3 changes by Parastais
vietnamese - 2 changes by nglekhoi


git-svn-id: http://svn.openttd.org/trunk@26139 6aa0318a-3be1-0310-93fa-89fd2396df07