There are eight regional archives in the Czech Republic, all of which can be accessed for free. This link from FamilySearch will give you the basic info, and links to them. https://www.familysearch.org/wiki/en/Czech_Republic_Archives_and_Libraries There are also maps that show the general coverage of each archive. The Genteam website has a gazetteer that tells you which archive has the records for the location you are interested in.
Each archive is different, on most you can down images, but at least one (Brno/South Moravia) you cannot, but you can take screen shots.
The archives are subject to the EU privacy laws, so modern records are not available from the archives.
I have used the archives for pre-1900 records. In some cases they go back to the early 1600s. It is remarkable what exists. The oldest records are usually in Latin, next is usually a German but this really depends on the location. With the progress of Czech nationalism, German was replaced by Czech.
I have copies of original documents from the 1880s to the 1930s and they are usually bi-lingual: Czech and German.