One has to remember that this particular style of helmet as mentioned by Jim was used postwar and by numerous European countries as well and there were post war variations also produced which included new liners and chin straps.
Here is the short list of Other countries that used Stahlhelm-type helmets this is in no way or form a complete list though as I can make case and point of other countries and organizations that they were used by.
Argentinaicon
Austria
Brazil: Firefighters Corps of Paraná State
Bulgaria
Chile
Colombia
Croatia
Czechoslovakiaicon
Denmarkicon
Estonia
Egypt
Finlandicon
Hungaryicon
Ireland
Latvia
Lithuania
Mexico
Norwayicon
Poland
Republic of China: M1935 Republic of China Army 1935–1950s?
Romania
Venezuela
Yugoslaviaicon
If you could possibly post a couple of other close up images of the buckle and the chinstrap ends including the rivets for attaching to the liner bails I will see if we can narrow it down a little farther for you .

Regards Mark