JavaScript
String.prototype.toLocaleNumber = function(x) {
var comma = this.indexOf(','),
period = this.indexOf('.'),
percent = ~this.indexOf('%'),
s = this.replace(/[^\d\-\.\,]/g, '');
if (comma !== -1 && comma < period) s = s.replace(/,/g, '');
if (period !== -1 && comma !== -1 && period < comma) s = s.replace(/\./g, '').replace(/,/, '.');
s = s.replace(',', '.');
if (percent) return parseFloat(s) / 100;
else return parseFloat(s);
};
console.info('Canadian (English and French) 4 294 967 295,123', '4 294 967 295,123'.toLocaleNumber());
console.info('Danish 4 294 967 295,123', '4 294 967 295,123'.toLocaleNumber());
console.info('Finnish 4 294 967 295,123', '4 294 967 295,123'.toLocaleNumber());
console.info('French 4 294 967 295,123', '4 294 967 295,123'.toLocaleNumber());
console.info('German 4 294 967.295,123', '4 294 967.295,123'.toLocaleNumber());
console.info('Italian 4.294.967.295,123', '4.294.967.295,123'.toLocaleNumber());
console.info('Norwegian 4.294.967.295,123', '4.294.967.295,123'.toLocaleNumber());
console.info('Spanish 4.294.967.295,123', '4.294.967.295,123'.toLocaleNumber());
console.info('Swedish 4 294 967 295,123', '4 294 967 295,123'.toLocaleNumber());
console.info('GB-English 4,294,967,295.123', '4,294,967,295.123'.toLocaleNumber());
console.info('US-English 4,294,967,295.123', '4,294,967,295.123'.toLocaleNumber());
console.info('Thai 4,294,967,295.123', '4,294,967,295.123'.toLocaleNumber());
console.info('Percentage', '98%'.toLocaleNumber());
console.info('Small Percentage', '12.32%'.toLocaleNumber());
console.info('Big Percentage', '1,238.02 %'.toLocaleNumber());