In a situation like:
My friend: 你知道StackExchange吗?
Me: 不知道啊, 孤陋寡闻了.
how can I properly translate 孤陋寡闻了 here? "I am being ignorant"?
你知道 StackExchange吗?
You know StackExchange?
不知道啊, 孤陋寡闻了。
Nope, I'm so out of touch.
"ignorant" means "lack knowledge", doesn't mean you are stupid or dumb, so translating "孤陋寡闻" as "being ignorant" is correct
However, "ignorant" is a derogatory term. If you don't want to be too harsh, you can translate "孤陋寡闻" as "ill-informed"
My friend: 你知道 StackExchange吗?
Me: 不知道啊, 孤陋寡闻了. (I'm so ill-informed)
~
ill-informed (adj):
not having a lot of knowledge especially about current news and events