When it comes to truth and culture, I've found it helpful to use the analogy of the lyrics and melody of a song. Here's what I mean:
Cultural Expression = Melody
In this analogy, the content of the gospel is the "lyrics" of the song and cultural expression is the "melody" of the song. The "lyrics" (gospel content) should never change. Truth transcends language, ethnicity and cultural expression. The gospel is the same whether it's proclaimed in China, the Sudan or the Bronx.
"Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand, and by which you are being saved, if you hold fast to the word I preached to you— unless you believed in vain. For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve."- 1 Corinthians 15:1-5
The objective facts concerning Jesus Christ's atoning death for sinners and glorious resurrection have always been a part of the gospel message and always will be. When these things are missing, the gospel is not being proclaimed. In addition to this, we would add the truth that salvation is by grace alone through faith alone in the finished work of Christ alone. This content would be the "lyrics" of the song in our analogy. If we are to faithfully proclaim the gospel, the lyrics must not change, regardless of the context.
At the same time, cultural expression varies. Cultural expression is the "melody". The sound of the "song" will be as varied as the amount of languages that are spoken. I should not expect the melodies of a Japanese gospel song to necessarily sound the same as the melodies of a gospel song in Trinidad.
"After this I looked, and behold, a great multitude that no one could number, from every nation, from all tribes and peoples and languages, standing before the throne and before the Lamb, clothed in white robes, with palm branches in their hands, and crying out with a loud voice, "Salvation belongs to our God who sits on the throne, and to the Lamb!"-Revelation 7:9-10
The beauty of God's design is that He is drawing a people to Himself that represent a staggering amount of diversity (vs. 9). And yet, the "lyrics" to the song are the same-"Salvation belongs to our God who sits on the throne and unto the Lamb!" (vs. 10)
Of course, we have a tendency to prefer our own "melodies"- the cultural expressions which are familiar to us. In turn, we look down on unfamiliar "melodies" and even attempt to make our "melodies" seem righteous compared to others. Some even try to make a case that certain "melodies" are inherently sinful- even without Scriptural support. But at the end of the day, the key question is if the "lyrics" match up with what the lyrics have always said. If so, Christians should at least be able to rejoice in that, even if the "melody" is strange or unfamiliar to us.
grace and peace,