add Czech translation

[codecov-io]

Codecov Report

Merging #185 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #185   +/-   ##
=======================================
  Coverage   93.89%   93.89%           
=======================================
  Files          14       14           
  Lines         459      459           
=======================================
  Hits          431      431           
  Misses         28       28

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[mlavin]

:rainbow: :rainbow: