Once you act on Rom 10:9, you are born again of holy spirit. You can then manifest it. ie: speak in tongues, along with the rest of the manifestations. If you are not born again, you cannot speak in tongues. Therefore, speaking in tongues is proof you are born again. Sadly, this does not mean that all who are born again will speak in tongues, but they could.
God's righteousness is an imputed gift (Rom 4:11) and the gifts of the Spirit are imparted gifts (1Cor 12:4-14). Imparted gifts can be given for a time and purpose (1Cor 13:8), but imputed gifts, like God's righteousness and eternal life (Rom 6:23), are permanent and put on the believer's account recorded in heaven (Gal 3:1-14, Rom 4). The imparted gifts are temporal and the imputed gifts are eternal. If we take that which is temporal and use it to justify that which is eternal, what have we done? We have made tongues and the manifestation of the gifts a form of righteousness and a measuring rod for salvation and being born again instead of faith in the blood of Christ. This is what the scriptures teach?...
Rom 10:6-17 6 But the righteousness which is of faith speaketh on this wise, Say not in thine heart, Who shall ascend into heaven? (that is , to bring Christ down from above) 7 Or, Who shall descend into the deep? (that is , to bring up Christ again from the dead.) 8 But what saith it ? The word is nigh thee, even in thy mouth, and in thy heart: that is , the word of faith, which we preach ; 9 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved . 10 For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation. 11 For the scripture saith , Whosoever believeth on him shall not be ashamed . 12 For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him. 13 For whosoever shall call upon the name of the Lord shall be saved . 14 How then shall they call on him in whom they have not believed ? and how shall they believe in him of whom they have not heard ? and how shall they hear without a preacher ? 15 And how shall they preach , except they be sent ? as it is written , How beautiful are the feet of them that preach the gospel of peace, and bring glad tidings of good things! 16 But they have not all obeyed the gospel. For Esaias saith , Lord, who hath believed our report? 17 So then faith cometh by hearing, and hearing by the word of God.
The righteousness that we have received from God comes by faith through the word (Rom 3:22, 10:17) and that is the evidence that we have from God that we are saved (Eph 2:8,9, Heb 11:1), not tongues or some gift, but faith in the cross of Christ. We receive the promise of the Spirit (Gal 3:14, Eph 1:13) when we believe and the Spirit bears witness with our spirit that we are the children of God (Rom 8:16). We may not understand this at first, being babes in Christ, but we grow in grace and knowledge and understanding of what Christ did for us through the finished work and we learn how to walk in the light and love of God as we are led by the Spirit through the word in the plan of God.