strings.xml

...
<string name="foo">Foo<annotation color="@color/dark_see_green" font="@font/montserrat_medium">bar</annotation></string>
...

TextViewExtensions.kt

fun TextView.applySpanAnnotations() {
    val annotations = (text as? SpannedString)
            ?.getSpans(0, text.length, Annotation::class.java) ?: return

        text = SpannableString(text)
                .apply {
                    loop@ for (annotation in annotations) {
                        when(annotation.key) {
                            "font" -> {
                                val fontName = annotation.value
                                val id = resources.getIdentifier(fontName, null, context.packageName)

                                if (id == 0) continue@loop

                                val typefaceSpan = CustomTypefaceSpan(ResourcesCompat.getFont(context, id))
                                setSpan(typefaceSpan,
                                        getSpanStart(annotation),
                                        getSpanEnd(annotation),
                                        Spannable.SPAN_EXCLUSIVE_EXCLUSIVE)
                            }

                            "color" -> {
                                val colorName = annotation.value
                                val id = resources.getIdentifier(colorName, null, context.packageName)

                                if (id == 0) continue@loop

                                val colorSpan = ForegroundColorSpan(ContextCompat.getColor(context, id))

                                setSpan(colorSpan,
                                        getSpanStart(annotation),
                                        getSpanEnd(annotation),
                                        Spannable.SPAN_EXCLUSIVE_EXCLUSIVE
                                )
                            }
                        }// when
                    }// for
                }// apply
}