A post card is small so people just write a short message to some friends about their holiday. A lot of people use abbreviations or text talk. Here is an example: Hi XXX, In Paris. Weather's G8. Seen Eiffel Tower, Louvre, Versailles. Doing Montmatre & Napoleon's tomb 2moro. Hotel's OK, near the metro. Hope you're all well.C u when I return nxt wk. YYYYYY.

What turn of speech use the English in the postcard? You mean to ask what type of speech to use when writing English on a postcard? I guess that would depend on who you are writing to, but in general, you don't need to write formally. Just write with 'casual' speech, meaning write as if you were speaking to someone in a conversation.