I once heard a boy complain with so much exasperation,"why should I bother myself with the way I speak the English language, as far as my message is understood,then am good to go".I replied him by saying."English Language has gained a prestigious and an indispensable status more than any other language in the globe,therefore your good usage of it especially the spoken aspect is very sacrosanct if we must break new grounds in our new world order.That does not mean our native languages are not relevant,infact they are our identity and heritage(every code has its domain of usage)
Now,what is Mothertongue interference?MT interference is the involuntary influence of one language on the other.MT interference is not a voluntary action,this phenomenon is always dominant in a multilingual situation,therefore the reason why Nigerians find it difficult to speak the queens English is not far fetched,it is because our native languages(L1) have influenced our English phonetic make up.
secondly,some phonetic sounds that are present in English phonemic system are abscent in the phonemic system of our local languages.eg,the consonant sounds in (think,this,bank) and the vowels in(her,burn,hunt,father),There we resort to what is called "phonemic substitution".sometimes I wonder why the Ghanians tend to speak the Received pronunciation(RP)better than we Nigerians.
Another aspect that poses a problem to us is supra-segmentals which is also a branch of phonetics and by supra-segmentals I mean stress and intonation.We find this aspect challenging because English Language is stress timed while our native langues are tonal in nature.Right stress placement goes a long way in determing if a word is a noun or a verb.for example: REcord(noun)-reCORD(verb)
In conclusion,we can improve our spoken English by visiting phonetic sound laboratories,undertaking speech therapy,downloading audio pronunciation exercises(peter Roach)and lastly cultivating the habit of tuning to BBC_____----Written by Daniel Egwahor(BA)English and Literature

It means our mother tongue is superior to the queen's english. Apart from Nigerians, check out a chinese or an indian speaking english and you will understand what I'm saying better. Your mother tongue is in your blood stream but the queen's english is a foreign body in your system.

PS: Even oyinbo people have the same mother tongue problem. Listen to oyibo man running commentaries during world cup when Nigeria is playing and see how they murder nigerian names.

The influence of Yoruba mother tongue on English language
http://articlesng.com/influence-yoruba-mother-tongue-english-language/

Mother Tongue Interference Problem of Students in Spoken English. A Case Study of Government Secondary School Township, Jos

Language whether, written, spoken, sign or spoken, or through any means is a tool for communication and English language out of the so many language of the world has emerged the most used language all over the world...

http://www.scharticles.com/mother-tongue-interference-problem-of-students-in-spoken-english/