//errormessages for en are already included in webshims core, this is only for information (by default en is equal to jQuery.webshims.validityMessages[""]):

jQuery.webshims.validityMessages.en = {
    "typeMismatch": {
        "email": "Please enter an email address.",
        "url": "Please enter a URL.",
        "number": "Please enter a number.",
        "date": "Please enter a date.",
        "time": "Please enter a time.",
        "range": "Invalid input.",
        "datetime-local": "Please enter a datetime."
    },
    "tooLong": "Please enter at most {%maxlength} character(s). You entered {%valueLen}.",
    "patternMismatch": "Invalid input. {%title}",
    "valueMissing": {
        "defaultMessage": "Please fill out this field.",
        "checkbox": "Please check this box if you want to proceed.",
        "select": "Please select an option.",
        "radio": "Please select an option."
    },
    "rangeUnderflow": {
        "defaultMessage": "Value must be greater than or equal to {%min}.",
        "date": "Value must be at or after {%min}.",
        "time": "Value must be at or after {%min}.",
        "datetime-local": "Value must be at or after {%min}."
    },
    "rangeOverflow": {
        "defaultMessage": "Value must be less than or equal to {%max}.",
        "date": "Value must be at or before {%max}.",
        "time": "Value must be at or before {%max}.",
        "datetime-local": "Value must be at or before {%max}."
    },
    "stepMismatch": "Invalid input."
};