Hi Diego,
you have to be more specific than just AES-128. Crypto is more complex and specifying a block cipher is not enough. At least you need to specify mode as well. ABAP AS has limited crypto API. Basically, it supports only PKCS#7. Here the message can be encrypted by AES-128 but key management is handled by asymmetric crypto. So my advice is to use this API. This will take care of every detail and you as a developer don't have to worry about anything.
If we are talking about a use case that you already have a key shared among parties and you want to encrypt a binary blob with AES then ABAP AS does not have implementation of AES available. Hence you can try a common workaround: OS command. You can dump a message as a file into a folder, encrypt it with some utility and then read it from there. This is not an ideal solution from security point of view.
Once i had to encrypt a short string with 3DES to generate a SSO cookie for some 3rd part system (not a great way how to do it but that's not important). ABAP AS contains a javascript engine (I know this sounds weird). Hence I found an implementation of 3DES in Javascript and used it to perform encryption. This is another workaround which you could use. Look for class cl_java_script (documentation).
Cheers