Every language use different 'registers' depending on the situation, the people involved, if it is written or spoken....
You can have a formal register (could you, would, if you please, dear sir....), informal register (please, can you, call me...), professional register e.g for a doctor (stetoscope, patient's notes, prescription)...
The word you are asking about is register, not registry. Register and registry are two different words. Register when used in the context of language means the level and style of writing or speech, that is appropriate to the situation it is used in. Register is generally divided into formal and informal. Take writing for example. A report is written in a formal register whereas a le