[KevinH]

In case anyone else wants to add this feature to their own code, here is the sample code:

import sys
from bs4 import BeautifulSoup
from PIL import Image

# extract base language from language code
def baselang(lang):
    if len(lang) > 3:
        if lang[2:3] in "-_":
            return lang[0:2]
    return None

def parse_xmpxml_for_alttext(xmpxml):
    xmpmeta = BeautifulSoup(xmpxml, 'xml')
    alt_dict = {}
    if xmpmeta:
        node = xmpmeta.find('AltTextAccessibility')
        if node:
            for element in node.find_all('li'):
                lang = element.get('xml:lang', 'x-default')
                alt_dict[lang] = element.text
                lg = baselang(lang)
                if lg:
                    alt_dict[lg] = element.txt
    return alt_dict


def get_image_metadata_alttext(imgpath, tgtlang):
    xmpxml = None
    description = ""
    with Image.open(imgpath) as im:
        if im.format == 'WebP':
            if "xmp" in im.info:
                xmpxml = im.info["xmp"]
        if im.format == 'PNG':
            if "XML:com.adobe.xmp" in im.info:
                xmpxml = im.info["XML:com.adobe.xmp"]
        if im.format == 'TIFF':
            if 700 in im.tag_v2:
                xmpxml = im.tag_v2[700]
        if im.format == 'JPEG':
            for segment, content in im.applist:
                if segment == "APP1":
                    marker, xmp_tags = content.split(b"\x00")[:2]
                    if marker == b"http://ns.adobe.com/xap/1.0/":
                        xmpxml = xmp_tags
                        break
        exif = im.getexif()
        # 270 = ImageDescription
        if exif and 270 in exif:
            description = exif[270]
    if not xmpxml:
        return description
    alt_dict = parse_xmpxml_for_alttext(xmpxml)
    # first try full language code match
    if tgtlang in alt_dict:
        return alt_dict[tgtlang]
     # next try base language code match
    lg = baselang(tgtlang)
    if lg and lg in alt_dict:
        return alt_dict[lg]
    # use default
    if 'x-default' in alt_dict:
        return alt_dict['x-default']
    # otherwise fall back to exif image description
    return description



imgpath = "test.jpg"
lang = 'en-US'
print(get_image_metadata_alttext(imgpath, lang))