Finding a reliable EX4 to MQ4 decompiler on GitHub is difficult because modern MetaTrader 4 (MT4) builds (600+) use advanced compilation techniques that are extremely hard to reverse
Metadata & provenance
Educational Disassemblers: Some developers host projects that attempt to "disassemble" the file into assembly-like code. While technically impressive, this won't give you a readable .mq4 file that you can edit and recompile easily. The Technical Reality: Decompilation vs. Recovery It is important to distinguish between two different goals:
Usability