There are many tongues and they can be classed in two main categories languages of men and languages of the elohim/aggelos/“angels”.
“If I speak in the tongues of men and of angels, but have not love, I am a noisy gong or a clanging cymbal.”
1 Corinthians 13:1
Tongues of men
Speaking in tongues of men by the Spirit can take place in several combinations.
Speaker in tongues of men
- the speaker utters the words and understands the new language
- The speaker utters the words and does not understand the new language
- The speaker utters the words and does not understand the words he utters but prays for the interpretation
Hearer of the tongues of men
- The listener hears the language and understands the language
- The listener hears the language and does not understand the language
- The listener hears the language, doesn’t understand it but through the gift of interpretation can interpret the language
As such with languages of men it is possible that someone will understand the language. Unless it is an ancient language or a language no longer in circulation.
Tongues of angels
Speaking in tongues of angels by the Spirit can take place in several combinations.
Speaker in tongues of angels
- The speaker utters the words and does not understand the new language
- The speaker utters the words and does not understand the words he utters but prays for the interpretation
Hearer of the tongues of angels
- The listener hears the language and does not understand the language
- The listener hears the language, doesn’t understand it but through the gift of interpretation can interpret the language
Language
Can changes in two ways, sound and meaning. You can have the same sounding word mean different things in different languages. Or you can change the sound but keep the meaning. Or you can change the sound and meaning
Examples
A chair sounds different in different languages but it means the same thing. Unless you understand to decipher the sound you could be talking about the same object but with different sounds/languages.
The sound is the same but the meaning is different.
Answering the question
1
Are the mysteries in the spirit that no one understands uttered in a language that can be interpreted via the gift of interpretation of tongues?
Yes provided the message is intended to be divulged to the listeners. If God intends for the message to be between the person speaking in tongues and God alone and God chooses not to relate to the speaker the message (so the mind can understand) but only allow the spirit of the man to be built up then, no the message will not be interpreted even by someone with the gift of interpretation.
2
Are the "mysteries in the Spirit that no one understands" still interpretable provided that someone with the gift of interpretation of tongues hears the utterances and interprets them?
Assuming that it’s not a human language that someone in the room can understand, assuming that the Spirit wants to divulge the mysteries, then yes someone with the gift of interpretation can interpret the message.
Does someone speaking in tongues automatically understand what they are saying?
No
“Therefore, one who speaks in a tongue should pray that he may interpret.”
1 Corinthians 14:13
If they already understand then this verse would have no place.
Babel like tongue
There are some speaking in tongues that are like the Tower of Babel, the speaker has a new language downloaded into their mind and they can now speak a language they have not previously known. As such they can translate what they have uttered but this isn’t usually how the mysteries in tongues is given, because at this point the mysteries could just be given directly in the language understood by all. This may or may not be the case for some or all those in Acts 2, namely that they now knew another foreign language. But it’s a possibility.
Interpretation
Interpreting is not the same as translating. Interpreting can convey the main message and idea of the message without translating word for word what was said. This needs to be understood because two people with the gift of interpretation can use two different interpretations but the same conclusion to convey the same message spoken in an unknown tongue.