1,can use my own language?           
yes.but only English support font selction,other language will be default font 31#(Arial)

2.how long to customize my jewelry?           
processing time within 2 days (work time)

3.how many letters can I put in ring?           
usually within 20 characters please

4.how many lines are suitable
3mm/4mm/5mm/6mm width:  1 line         
8mm width:  2 lines
10mm width:  3 lines         
12mm width:  4 lines
15mm width:  5 lines

Example
font 35 , info: MG-12