1) The custom is to perform “Releasing of vows” on the eve of Rosh Hashanah. One who does not understand the wording in the holy tongue, should say it in a language which he understands. (Kitzur Shulchan Aruch 128)
2) A person should be very careful to say the words of prayer correctly. It follows that a person should be very careful to try to find a prayer book which has been properly proofread to use for praying. (ibid 129)