[Feature] Latvian localization

[EPoikans]

What problem does this feature solve?

Add latvian localization to echarts

What does the proposed API look like?

From apache/superset this code block would not error when trying to localize superset to latvian.

const loadLocale = async (locale: string) => {
  let lang;
  try {
    lang = await import(`echarts/lib/i18n/lang${locale}`);
  } catch {
    // Locale not supported in ECharts
  }
  return lang?.default;
};

[EPoikans]

I am willing to make a PR for the localization as I am latvian.

[plainheart]

@EPoikans Thanks! Feel free to open a PR to add this locale.