When MQL5 is the natural choice
MQL5 runs inside MetaTrader 5 and has direct access to symbols, orders, positions, indicators and terminal events.
MT5 provides a native environment for testing Expert Advisors and parameterized trading logic.
For a Forex system whose execution lives entirely inside MT5, keeping the core execution layer in MQL5 reduces unnecessary infrastructure.
When Python is the natural choice
Python is well suited to REST and WebSocket integrations used by crypto exchanges and other external services.
It has a broad ecosystem for data processing, databases, web services, monitoring and custom infrastructure.
A Python engine can run as a service on a VPS without depending on an MT5 chart lifecycle.
A hybrid architecture can be useful
The choice does not always need to be binary. MT5 can remain responsible for broker-side execution while a Python or web service handles selected monitoring, analytics or external integrations. The important part is to define a narrow, authenticated interface between components.
The decision checklist
Choose based on execution venue, required APIs, deployment environment, persistence requirements, monitoring needs and who will operate the system. Technology should follow the workflow rather than force the workflow to fit the technology.