I think starting around Windows 7, Microsoft’s OS let you switch languages freely, even with lighter editions. I remember buying a budget (less than 200 euros) Windows 7 laptop in France with the barebone license bundled a few years ago, and switching to English and Japanese without any issue. I had no issues with this and Windows 8.1 either, so I hope they kept that policy intact for Windows 10.
Edit: Ah, I seem to remember I may have had to download the Windows install files from MS back then. They provided them freely. It seems they keep providing such install files for Windows 10, and one of the option is “single language” - thus I’d guess the default version is bundled with multiple ones.