Well, it’s not illegal to quote a foreign word when speaking Esperanto. So it’s perfectly fine to say for example: Lia familia nomo estas “Walker”. (‘His surname is “Walker”.’) or Ŝi naskiĝis en la provinco 广东 (Gŭangdong) en Ĉinujo. (‘She was born in the Guangdong province in China.’), and to pronounce those foreign words to the best of one’s abilities.
But every language has a set of phonotactic constraints that describe how the sounds may be combined to form proper words in that language (native or naturalised borrowed words) — in Japanese one such rule would be that every syllable must end with a vowel or with a vowel followed by ⟨ん⟩ /n/, in English one such rule is that ⟨ng⟩ /ŋ/ cannot begin a syllable, and in Esperanto one such rule is that ⟨ŭ⟩ /w/ must immediately follow ⟨a⟩ or ⟨e⟩ in the same syllable.
So all fully esperantised words undergo slight natural changes that make them conform to the Esperanto phonotactic constraints. One such change is that the sound /w/ in illegal positions often becomes /v/. So for example the Esperanto name of the capital of the US is Vaŝingtono and the traditional Esperanto name equivalent to the English name “William” is Vilhelmo.
Well, the sentence with oni would also make sense, but there's nothing wrong with personal one with vi. The intonation of the speaker fits non-generalised version, where for example someone informed him he's about to buy seven cars (or seventh car, for that matter) and the speaker wants to show his astonishment and criticise that idea.