Hello, I am Helen Zhang, a professional Chinese teacher from eChineseonline.
Please see the translation for the Mandarin sentences you asked below:
Excuse me: 对不起(duìbu qǐ)
May i ask you: 请问(qǐngwèn)
What nationality: 你是哪国人？(Nǐ shì nǎ guó rén?)
A little: 一点儿 (yìdiǎnr)
That’s all right: 不客气 (búkèqi)

Please read the following dialogue:
   Duìbu qǐ, qǐn wèn nǐ shì nǎguǒ ren?
A: 对不起，请问你是哪国人？
   Excuse me, may I ask what you nationality is?
   Wǒ shì Yīnguóren. Wǒ zhí huì yìdiǎnr Hànyǔ.
B: 我是英国人。我只会一点儿汉语。
    I am British. I can only speak a little Chinese. 
    Méiguānxi. Wǒ kěyǐ,  bāng nín fānyì.
A: 没关系。我可以帮您翻译。
   It doesn’t matter. I can be the interpreter for you.
   Xièxiè.
A: 谢谢。
   Thanks.
    Búkeqi.
B: 不客气。
    That’s all right.