If in a discussion, one were to say something correct and you were to further confirm the truthfulness of that statement and back him up, we say in my mother tongue 'in confirmation to your saying/ or in credibility' and then go along to say something relevant to his story, but I feel as if they don't cut if for me. They seem unsuitable.
Both formal and informal answers are welcome. Thank you.
Simply prefix your follow-up statement with:
Furthermore, ...
This is perfectly acceptable in both formal and informal contexts.
Indeed
Merriam-Webster: used when making a statement that adds to or strengthens a previous statement
Macmillan: used for adding a statement that supports and increases the effect of what you have just said
Dictionary.com: in fact; in reality; in truth; truly (used for emphasis, to confirm and amplify a previous statement, to indicate a concession or admission, or, interrogatively, to obtain confirmation)
Friend: Temper curiosity with wisdom.
You: Indeed, my experimentation with smoking was foolish.
Probably, "bear testimony to"(idiom)
If something bears testimony to a fact, it proves that it is true.
Testifying is serious business, but it doesn't always happen in court: If someone knows you're good at math, they can testify to your math skills. Or if you've been to a restaurant, you can testify to your friends that it has awesome desserts. (TFD)
A more informal way might be 'As you said, ...' or 'Like you said, ...'
