How can I offer advice to invite a Czech girl to Islam, especially given her need for sources in the Czech language and the difficulty of explaining rulings on alcohol, fornication, and mixing?

You must thank Allah for the interest in inviting the girl to Islam, along with supplicating for her guidance. It is important to be cautious when guiding someone to translate the meanings of the Quran, and to search for reliable translations. One can consult trusted Islamic centers or reliable callers to Islam in the country of residence to inquire about translations of the meanings of the Quran in Czech, if available. The girl can be guided to learn Islam in the language she knows, or by learning other common languages like English and French to benefit from Islamic websites. However, the first and best option is for her to learn the Arabic language to fully understand the Quran and the rulings of Islam.