I really don't want to be destructive and undo other people's work, but again I think this list is not getting better by making it longer - I'm especially referring to the Switzerland section.  
 * AlpTransit Gotthard (ATG) This is the company that buils the Gotthard Base Tunnel. It does not operate it, so it is for sure no railway company. Even IF they did operate the Gotthard base tunnel, it would not be a mountain railway, because as the name suggests, a base tunnel does not climb a mountain. I removed that entry. 
 * Sihltal-Zürich-Uetliberg-Bahn I already wrote what I think is wrong with that entry. I rearranged it. 
 * we don't need an entry for Lötschbergbahn if we have an entry Bern-Lötschberg-Simplon railway (-> removed) 
 * Should we list names of railway companies (like RhB), or rather particular railway routes? An extreme example is the SBB-CFF-FFS. Sure they have some routes in the mountains (for example the Gotthardbahn), but I wouldn't call SBB a mountain railway. The same is true for BLS, SZU, SOB, to some extent RhB (the Bernina route surely qualifies as mountain railway, the Albula route possibly, Landquart-Chur for sure doesn't), and probably others. I think the latter definitely makes more sense wherever applicable, but that would produce some uncommon names for railway routes (Simplonbahn?). Anyway, I'm not happy at all the way it is. 
 * There are many entries (some admittedly by me) where I wonder wheter they make sense. Is railway that does not fully climb a mountain, but uses a tunnel to pass under it, really a mountain railway (i.e. Gotthardbahn, Lötschbergbahn)? 
 Finally, I don't like the article's definition of mountain railway at all. "[...] that ascends and descends [...]" so if there is only one track to climb the mountain (in case its not a pass, but rather a railway to carry tourists to the top of a mountain), it is no mountain railway according to the definition? (does not make sense) Or a railway that is built through the mountains but does not have big inclines is no mountain railway either? (possibly makes sense, I don't know how a native english speaker interprets "mountain railway"). 
 German speakers, compare the terms "Bergbahn" and "Gebirgsbahn". The former climbes a mountain, the latter just somehow runs through mountainous terrain. Maybe there is a similar distinction in english. In german, RhB would never be generally called a "Bergbahn", however it clearly is a "Gebirgsbahn". 
 Sorry to bother you with that much text on so little details, but I feel that the article fails to adress some basic questions and thus needs some work. I can't do it because I don't know what exactely the article is supposed to say.