If that brother speak in tongues and another interpret or a foreigner understood him, I would believe that brother has the real God's gift of tongues.
But when a brother insists that tongues can also be for private use, he is still my brother, but that supernatural tongue as gained by another filling of the Holy Spirit, is not of Him at all and that includes that other apostate calling of seeking another baptism with the holy Ghost with evidence of tongues as not of Him either for how he had gained that tongue for private use & why that tongue never comes with interpretation.
Indeed, some believe interpretating tongues is by getting the gist or feel of what is being said in that gibberish nonsense as Joyce Meyers has testified but they are not really interpreting that tongue at all for why it is just gibberish nonsense and not any language of men at all.
Since the purpose of the gifts of the spirit & the manifestations of them is to profit the body of Christ for why tongues will come with interpretation in the assembly to profit the body withal, then tongues can never be for private use. ( and they have by citing all the benefits for private use that one wonders why they go to the assembly at all as if they need no other body when they can do all those things and yet without interpretation to never understand what is going on with that tongue ? )
1 Corinthians 12:4 Now there are diversities of gifts, but the same Spirit. 5 And there are differences of administrations, but the same Lord. 6 And there are diversities of operations, but it is the same God which worketh all in all. 7 But the manifestation of the Spirit is given to every man to profit withal....
19 And if they were all one member, where were the body? 20 But now are they many members, yet but one body. 21 And the eye cannot say unto the hand, I have no need of thee: nor again the head to the feet, I have no need of you.
The verses above proves why tongues can never be for private use in the assembly or individually anywhere when that tongue speaker needs someone to interpret that tongue so he can understand it for that tongue to be fruitful to himself.
So that is why believers re not to believe every spirit but test them by knowing He is in us so that spirit that comes over us later after salvation, is not the Holy Spirit (
1 John 4:1-4 ) for why they are even to test the tongues as well because the world's supernatural tongue is just gibberish nonsense. (
1 John 4:5-6 &
Isaiah 8:19 )