MQL stands for MetaQuotes Language, which is the programming language used to develop the programs supported by MetaTrader terminals. The number at the end of MQL specifies the version of MetaTrader terminal related to it. So if you need to build a MT4 program then you must develop it using MQL4, and if you need a program for MT5 then you must use MQL5.
Although both MQL4 and MQL5 are based on C++, until build 600 of MetaTrader terminal, MQL4 was a language more basic and elemental than MQL5, but starting from that build hardly any differences are between them. In fact, both MQL4 and MQL5 have not been fully merged mainly because of the vast number of programs developed over MQL4, which are incompatible with MQL5. So currently, MQL4 programming and MQL5 programming are basically the same with just some small differences. Henceforth, whenever we mention MQL4 we will refer to both of them MQL4 and MQL5.
We have excellent MT5 and MT4 programmers which can develop any tool (EA, Indicator and Script) for any of those platforms. They can also convert any code between MQL4 and MQL5. So don’t hesitate to ask a free quote for your project here.