There are 25 people and AT LEAST one of them speaks all three languages.
We are trying to find the people who can interact with each other in English and German. That means these people can either speak English and German or English, German and Spanish.
So we need to find the number of people that fall under these two categories.
Let's look at the remaining information
1) 4 people speak two languages but not Spanish ==> this is enough for the first category( i.e. the people that speak English and German only), but we do not know how many people speak all three languages (the question stem says AT LEAST one person)
INSUFFICIENT
2) One fifth of the group speaks more than one language. ==> let's break this down.
one fifth of the group is 25/5 = 5 people. 5 people speaks more than one language. We do not know how many of these people speak only English and German or all three languages.
INSUFFICIENT.
Now let's look at both informations together.
We know that 4 people speak English and German, and only 5 people speak more than one language(i.e. 2 languages or 3 languages). The information in question stem indicated that there is at least one person who speaks all three languages, but with these information we can definitely say that there is exactly one person who speaks all three languages. Thus determining that 5 people can interact with each other in English and German.
Answer:C
Hope this helps.
Cheers