Hi there. I speak in tongues, and have have interpretations of another persons tongues on occasion.
The times I have had an interpretation, its been more of an 'impression' for me -- and as I begin to speak, more flows out. It usually has been backed up by another person present either with a similiar impression, or a scripture to correspond with it.
I have also known a few, maybe two at most, interpret their own tongues. I feel like God can do that; why not? I also know that if the interpretation doesn't bear witness to me, or resonate within my own spirit, its not for me to lay hold of.
As I write this, I also cannot think of an intpretation that has been anything but glorifying or praising or giving thanks to God.
so if its about praising the Lord, its all good. If someone is speaking out during a gathering, the issue is their maturity and appropriate timing. Speaking in tongues, and any using other spiritual gift requires good mentoring from a trusted, mature, faith filled believer.
As for speaking tongues, I believe that my tongue is an actual language here on earth. At different times, by tongue is not the same. For example, when I know I am praising God, my tongue is always the same --- the same when I am praying over something/someone, I will pray in the spirit until God releases the english words to pray for someone. (prayer ministry is also always for building up and edifying) When there has been spiritual opposition present, my tongue has been very different.
I don't have conscious control over the change.
Hope this helps with your information gathering.
PS -- I need to add something, tongues from someone else is not to be trusted as a prophetic word etc. Like anything, our individual relationship with the Lord is paramount. So, the real issue is, if you feel the person may be faking it etc. is to not hold that person in judgement. (see how easy the devil wants to split the church and divide relationship?)
Praying in the spirit is for edifying oneself; its like a heavenly hug that just builds and builds your spirit.
When I spend time with the Lord praising him in the spirit, I feel full to overflowing with his love, mercy, etc etc. etc.
Blessings to you.