Can I make a dialogflow chatbot in English and then somehow change it's language settings to convert it to support other languages like Italian, Spanish etc? I mean except language settings do I have to make any other changes in dialogflow?
You can add additional languages to your bot through the language settings in Dialogflow.
When you add a new language Dialogflow will copy all intents and fill in example phrases for every system intent that you use. Any custom intents that you made will also be copied, but these won't have any example phrases for the new language, so you have to add new example phrases in the new language for them.
If you use any entities you will also have to add new values in the new language any custom entities that you made.