Add locale (i18n) support

[lidel]

New source dataset format introduced in #80 provides country and city names in other languages than English
(at the time of writing this, we have names in: de, en, es, fr, ja, pt-BR, ru and zh-CN).

We could add support for passing optional language code to the lookup method.

Details of how to modify b-tree format remain TBD.

Open questions:

• should we have separate b-tree for each language, or should we keep all translations in a single tree?
  • if it is a single tree, how to ensure client is not fetching strings that they do not need?

[lidel]

fwiw source CSV identified by DATA_HASH in src/generate/index.js includes a few locales:

$ ipfs ls bafybeicfcxk4bx3nwmg3hwjmlc6n2qzn73mfm5itfpadwh5w7bux2chgz4
bafkreihes7r7nzovjeihybcvm7r4wofc4raq4auw56ufn2dnte4tioso2e 55        COPYRIGHT.txt
bafybeihdsvtywrrbmoqisqrltapw2zbgbu5tl6x5ijjmrauo6boeqo3vay 218942111 GeoLite2-City-Blocks-IPv4.csv
bafybeibvkpyxiad2at2ld4hgjat2boqkpolg3niqekp67fugrnp4pbvihi 80894247  GeoLite2-City-Blocks-IPv6.csv
bafybeicrybijxosuh4l4mrtfc6hi4ey6rvv5pluqhnqzdozqkk34svp4yy 8730908   GeoLite2-City-Locations-de.csv
bafybeiatzmaijbha4n6fmfqiy3vm4k62k5jbeu27rtkdcdjhgslcadxqqa 10432599  GeoLite2-City-Locations-en.csv
bafybeifqloagg3fjnyt5loeac4j2xl6nuav4mgywkk5x7tqe6exxirv2wy 8663321   GeoLite2-City-Locations-es.csv
bafybeiaqi4ayqxex2y4szinily32bah2vahhbkxb6j2xiamtpf7am56kte 9258315   GeoLite2-City-Locations-fr.csv
bafybeiguklag6kpmr3nvtrqrthj7m4lhi5dst4ems25h2mdswkgzultnxa 11645375  GeoLite2-City-Locations-ja.csv
bafybeie2hoxesntzwzwrpzeaxrb3wiudgoy2j3a2umnb5jyqom7s6zkyiu 8668327   GeoLite2-City-Locations-pt-BR.csv
bafybeic5yeidvb7dsreanhhlxllm7wacnkbwwrczcjk5o3hzayl3lznuva 11729812  GeoLite2-City-Locations-ru.csv
bafybeicvkmkdettefag6ai6v6uwf5hp6f2knjlvwpqsrdpgbk6ieuruca4 9019475   GeoLite2-City-Locations-zh-CN.csv
bafkreic7pswr7zmeynivapbgoi44p5fauyhofvfhhidefqhxziixfuqvom 398       LICENSE.txt

We are not using them during b-tree generation, but we could store a map with Location names in available locales, and either accept optional language code as new lookup parameter, or simply return them as a Locales map.