Thymeleaf - i18n get back the template by locale and custom parameter

Question

Circumstances

I'm using Spring Boot with Thymeleaf for populating my HTML template files and get back the result as a String. For that I used SpringTemplateEngine.

The code looks like this

    Context context = new Context();
    context.setVariables(myProperties);
    return templateEngine.process(htmlTemplateName, context);

The problem

For i18n I have a different approach. My thymeleaf HTML template namings are the following (similar to Freemaker templating):

templatename_default_FOO.html
templatename_en_EN_FOO.html
templatename_de_DE_FOO.html

templatename_default_ANOTHER.html
templatename_en_EN_ANOTHER.html
templatename_de_DE_ANOTHER.html

The convention is:

• templatename - is the name of the template
• default/en_EN/de_DE - is the locale which I get from an API - The locale may not exists in the templates, in this case I want to use the default template with the matching user parameter
• FOO/ANOTHER - different parameter values which the users sets - they exists in atleast one template's name (the default should contain it)

Previously I used ResourceBundles to get the templates by locale if existed, otherwise the default value was automatically chosen. However with Thymeleaf implementation I don't know how to implement the same mechanics, because currently I get the template by providing the full name. If I add a locale which not exists I don't get back the default template.

Question

I know that i18n in Thymeleaf is done through language.properties, but in my case I would need a function where I provide the template name, the locale and the user parameter and I get back the specified HTML file if exists and if not the default HTML file with the matching user parameter.

Something similar:

public String getTemplate(Map<String, Object> myProperties, String templateName, Locale locale, String userParameter) {
    Context context = new Context();
    context.setVariables(myProperties);
    return templateEngine.process(templateName, locale, userParameter  context);
}

Is that possible somehow or I should use language.properties? Or I should write custom logic to check if the template not exists go with the default one?

Thanks in advance