I am in Czechia as well and I never had this problem. Searching in English gives me relevant results (about the same as if I was in the USA) and searching in Czech gives me Czech results. Shopping works OK even with English searches - I'd get English speaking Czech shops or German/UK Ebay and Amazon.

I have all computer/browser locales set to US English, Google uses that but I remain on the .cz site. Works flawlessly.