Cyimking wrote If it's API based, you can use any language that you want. My suggestion is that you use an API wrapper instead of writing one yourself. However, you are free to use any language that you want.

Step 1: Select a language that's comfortable for you. It can be PHP, JS, Java, C, etc...
Step 2: Build the bot/application with dummy data. Just build it so it can send over data to discord.
Step 3: Integrate the COD API.
Step 4: Set up observers, events, and or cronjobs to automatic the data.

Of course, you will have to design the bot to be scalable, secure, and efficient.

Overall, start simple then add as you go -- no need to make an overcomplex bot.

Suggestion
Use a discord sdk (REST API client). Save you all the troubles of building one yourself. You just have to configure the sdk then call the correct functions! Boom. Done.