Personal, commercial or investment banking are all part of the global financial system in which language skills will give you more options in getting on. Foreign banks, customers and investors probably speak English, but languages are a skill which could make you stand out. If you manage foreign customers or deal with international banking, being able to deal with your colleagues and customers in everyday working language will give you more confidence and an advantage. If you seek positions in the area of banking, your language skills may be what gives you access to a successful path. Online application forms for investment banking analyst often have a section asking you to select all the languages you have some ability in.
Ireland is an international financial centre. It is hard to come across as international if you cannot speak any other language but English. Be the one who is truly international by being able to connect with people. If you are fluent in a foreign language, see which recruiters will value it and what opportunities they might offer you.