The developer hosts the game on a Polish domain (https://soldat.pl/), and even has a FAQ entry regarding the name: https://soldat.pl/en/page/faq

Q: What does "Soldat" mean!?

A: "Soldat" or "Soldaat" means "soldier" in the following languages: german, dutch, norwegian, swedish, danish, french, slovenian, afrikaans, russian, catalan and romanian.